Accessing the long-lived emissive 3IL triplet excited states of coumarin fluorophores by direct cyclometallation and its application for oxygen sensing and upconversion

Article abstract of DOI:10.1039/c1dt10344j

We studied four cyclometallated Pt(ii) complexes, in which the thiazo-coumarin ligands (Pt-2, Pt-3 and Pt-4) or the phenylthiazo ligand (Pt-1) were directly cycloplatinated. Pt-2 shows intense absorption in visible region but other complexes show blue-shifted absorption. Room temperature phosphorescence was observed for all the complexes, and the emission wavelength is dependent on the size of the π-conjugation, not the intramolecular charge transfer (ICT) feature of the CN ligands. Pt-2 shows longer phosphorescence lifetime (τ = 20.3 μs) than other complexes (below 2.0 μs). Furthermore, Pt-2 shows phosphorescence quantum yield Φ = 0.37, whereas Pt-3 and Pt-4 show much smaller Φ values (0.03 and 0.01, respectively). DFT/TDDFT calculations indicate ³IL triplet excited states for the complexes. The complexes were used as for luminescence O₂ sensing and triplet-triplet-annihilation (TTA) based upconversion. Stern-Volmer quenching constant K_SV = 0.026 Torr^-1 was observed for Pt-2, ca. 89-fold of that of Pt-3. TTA upconversion is achieved with Pt-2 (λ_em = 400 nm with λ_ex = 473 nm, anti-Stokes shift is 0.47 eV, excitation power density is at 70 mW cm^-2). The upconversion quantum yield with Pt-2 as triplet sensitizer is up to 15.4%. The TTET efficiency (K_SV = 1.33 × 10⁵ M^-1, k_q = 6.57 × 10⁹ M^-1 s^-1. DPA as quencher) of Pt-2 is 34-fold of the model complex [Ru(dmb) ₃][PF₆]₂. Our results show that the ³IL state can be readily accessed by direct cyclometallation of organic fluorophores and this approach will be useful for preparation and applications of transition metal complexes that show intense absorption in visible region and the long-lived emissive ³IL excited states.

Full text of DOI:10.1039/c1dt10344j

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PAPER
3
Accessing the long-lived emissive IL triplet excited states of coumarin
fluorophores by direct cyclometallation and its application for oxygen sensing
and upconversion†
Wenting Wu, Wanhua Wu, Shaomin Ji, Huimin Guo and Jianzhang Zhao*
Received 1st March 2011, Accepted 21st March 2011
DOI: 10.1039/c1dt10344j
We studied four cyclometallated Pt(II) complexes, in which the thiazo-coumarin ligands (Pt-2, Pt-3 and
Pt-4) or the phenylthiazo ligand (Pt-1) were directly cycloplatinated. Pt-2 shows intense absorption in
visible region but other complexes show blue-shifted absorption. Room temperature phosphorescence
was observed for all the complexes, and the emission wavelength is dependent on the size of the
Ÿ
p-conjugation, not the intramolecular charge transfer (ICT) feature of the C N ligands. Pt-2 shows
longer phosphorescence lifetime (t = 20.3 ms) than other complexes (below 2.0 ms). Furthermore, Pt-2
shows phosphorescence quantum yield U = 0.37, whereas Pt-3 and Pt-4 show much smaller U values
3
(
0.03 and 0.01, respectively). DFT/TDDFT calculations indicate IL triplet excited states for the
complexes. The complexes were used as for luminescence O
TTA) based upconversion. Stern–Volmer quenching constant KSV = 0.026 Torr was observed for
Pt-2, ca. 89-fold of that of Pt-3. TTA upconversion is achieved with Pt-2 (lem = 400 nm with lex
2
sensing and triplet–triplet-annihilation
-
1
(
=
-
2
4
73 nm, anti-Stokes shift is 0.47 eV, excitation power density is at 70 mW cm ). The upconversion
5
-1
quantum yield with Pt-2 as triplet sensitizer is up to 15.4%. The TTET efficiency (KSV = 1.33 ¥ 10 M ,
9
-1 -1
k
q
= 6.57 ¥ 10 M s . DPA as quencher) of Pt-2 is 34-fold of the model complex [Ru(dmb)
Our results show that the IL state can be readily accessed by direct cyclometallation of organic
3
][PF ] .
6
2
3
fluorophores and this approach will be useful for preparation and applications of transition metal
3
complexes that show intense absorption in visible region and the long-lived emissive IL excited states.
3
9
Introduction
therapy), and more recently triplet–triplet-annihilation (TTA)
40–44
based upconversions.
in most of the applications is the triplet–triplet-energy-transfer
TTET) process.
will improve the TTET efficiency.
lifetimes of the triplet excited state of the typical cyclometallated
Pt(II) complexes are less than 2 ms.
absorption of typical cyclometalated Pt(II) complexes are weak
in visible region. Thus, preparation of Pt(II) complexes that show
intense absorption in visible region and long-lived triplet excited
states is important for improvement of the applications of these
materials. Surprisingly no systematic studies have been carried out
The principle photophysics involved
Ÿ
1–15
Ÿ
Cyclometalated Pt(II) complexes with C N ligands,
Pt(II) bisacetylide complexes,
and N N
1
6–31
have attracted much atten-
14,34
(
In this case longer triplet excited state lifetime
tion. The emissive excited state of these complexes are usually
14,34
However, the intrinsic
3
3
MLCT/ IL (metal-to-ligand-charge transfer, or intraligand).
The long-lived triplet excited states of these organometallics
are in particular interesting because many of the applications
of transition metal complexes are closely related to the triplet
excited states, such as electroluminescence or the luminescent
1,5,9,45–46
Furthermore, the
1,12–15
O
2
sensing.
Furthermore, very often the applications can
be enhanced with the long-lived triplet excited states, such as in
efficient photo-induced charge separation (for dye sensitized solar
cell or artificial photosynthesis),
probe (e.g. luminescent oxygen sensing or thiol probes),
photocatalysis, sensitization of singlet oxygen (for photodynamic
Ÿ
to enhance the visible-light absorption of the C N cyclometalated
2
4,32–34
lifetime-based molecular
Pt(II) complexes and to extend the triplet excited state lifetimes
of the cyclometallated Pt(II) complexes. Furthermore, we noticed
the cyclometalated Pt(II) complexes have not been used for oxygen
sensing and upconversions.
1
4–15,35–37
38
It has been shown that the excited state lifetime of Ru(II)
Ÿ
State Key Laboratory of Fine Chemicals, School of Chemical Engineering,
Dalian University of Technology, Dalian, 116024, P. R. China. E-mail:
zhaojzh@dlut.edu.cn; Fax: +86 411 8498 6236; Tel: +86 411 8498 6236
and N N Pt(II) bisacetylide complexes can be substantially
prolonged, especially by tuning the triplet excited states of the
complexes.
state lifetime is to access the IL excited state, which usually shows
longer lifetime than the MLCT excited state.
14,18,27,35,47–53
One approach to prolong the triplet excited
†
Electronic supplementary information (ESI) available: Preparation of
the sensing films, structural characterization spectra and determination of
the upconversion quantum yields. See DOI: 10.1039/c1dt10344j
3
3
16,26–28
Previously
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Scheme 1 Synthesis of the cyclometalated Pt(II) complexes Pt-3 and Pt-4. The molecular structures of the known complexes Pt-1 and Pt-2 and the
polymer used for oxygen sensing (IMPEK-C), and the triplet acceptor/annihilator 9,10-diphenylanthracene (DPA) used in the upconversion are also
◦
shown. (i) piperidine (0.05 eq.), MeOH, reflux 4–5 h. (ii) a) PtCl
r.t. overnight. (iii) a) tert-BuLi, THP, 0 C, 4 h; b) THP/DMF (1 : 1, v/v), r.t., overnight, HCl.
2
(1.6 eq.), 2-methoxyethanol/benzonitrile 140 C, 1 h; b) Hacac (9.0 eq.), EtN
3
(9.0 eq.)
◦
Ÿ
coumarin was used as C N ligand to prepare cyclometalated
Pt(II) acac complexes, phosphorescence lifetime up to 20.3 ms was
emission wavelength and lifetimes, no detailed study has been
carried out to reveal the component of the T state. Furthermore,
the characteristic photophysics of Pt-2, such as the intense
1
9
observed (Pt-2, Scheme 1). However, the previous investigation
on Pt-2 was limited to the photophysical properties such as the
absorption in visible region, high phosphorescence quantum yield
5
954 | Dalton Trans., 2011, 40, 5953–5963
This journal is © The Royal Society of Chemistry 2011

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1
and long-lived triplet excited state, have never been employed for
applications.
We have been interested in photophysics of luminescent
84.4%. H NMR (400 MHz, CDCl
3
): d 9.09 (s, 1H), 8.11 (d, J =
8.4 Hz, 1H), 8.00 (d, J = 8.0 Hz, 1H), 7.75 (d, J = 7.6 Hz, 1H), 7.65
(t, J = 8.0 Hz, 1H), 7.55 (t, J = 8.0 Hz, 1H), 7.47–7.44 (m, 2H),
7.40 (t, J = 7.6 Hz, 1H). EI-HRMS m/z: calcd for C16
1
2,13
transition metal complexes.
Inspired by some pioneering
H
9
NO S
2
51,53
+
◦
works,
complexes,
Pt(II) with naphthalimide, and prepared phosphorescent molec-
we prolonged the triplet excited state lifetime of Ru(II)
([M] ) 279.0354, found 279.0363. M.p. 220.9–222.0 C
35,54
tuned the emission properties of cyclometalated
Synthesis of Pt-3. PtCl
in 1 mL of benzonitrile by heating at 160 C for several minutes. L-
(80.0 mg, 0.31 mmol) in 2-ethoxyethanol (6 mL) and benzonitrile
2
(129.0 mg, 0.49 mmol) was dissolved
14
◦
36
ular probes for detection of thiols. We also prepared complexes
with long lived IL excited states for Pt(II) bisacetylide complexes.
3
(
3
55
18 mL) was added via syringe. The mixture was heated for 1 h
Herein we prepared two new cyclometallated Pt(II) acac com-
plexes with the coumarin subunits directly cyclometallated (Pt-3
and Pt-4, Scheme 1), with the aim to access the visible-light har-
vesting Pt(II) complexes that show long-lived triplet excited states,
and to study the relationship between the molecular structure
and the emission properties. Room temperature phosphorescence
were observed for all the complexes. The complex with the
diethylamino appendant on the coumarin moiety (Pt-2) gives the
longest luminescent lifetimes, whereas the complexes without the
diethylamino substituents give short luminescent lifetimes (Pt-3
and Pt-4). The emissive triplet excites states of the complexes
with coumarin subunits (Pt-2, Pt-3 and Pt-4) were assigned
◦
at 140 C. The solution was cooled and diluted with 7 mL of
acetone. Then, 276 mL of Hacac and 361 mL of triethylamine were
added and the solution was stirred overnight at r.t. Then 25 mL of
hexane were added and the precipitate was collected by filtration.
The product was purified by column chromatography (silica gel,
CH
0.0 mg, 17.7%. Decomposition temperature: 270 C. H NMR
400 MHz, CDCl ): d 9.16 (d, J = 8.4 Hz, 1H), 8.98 (d, J = 8.0 Hz,
H), 7.78 (d, J = 8.0 Hz, 1H), 7.49 (t, J = 8.0 Hz, 1H), 7.51–7.38
2
Cl
2
: triethylamine = 100 : 2, v/v). Orange solid was obtained,
◦
1
3
(
3
1
(
m, 2H), 7.22–7.20 (m, 2H), 5.57 (s, 1H), 2.04 (s, 3H), 1.96 (s, 3H).
MALDI-HRMS m/z: calcd for C21 SPt ([M]+) 572.0370,
found 572.0391. Anal. Calcd. For C21 PtS: C, 44.06; H,
.64; N, 2.45; Found: C, 44.17; H, 2.79; N, 2.42.
H
15NO
15NO
4
H
4
3
as IL (intraligand) excited state. We investigated the triplet-
2
3
energy-transfer of the IL excited state of these complexes, i.e.
for luminescent O
based upconversion.
2
sensing and triplet–triplet annihilation (TTA)
58
Synthesis of 2-Hydroxy-3-naphthaldehyde
Under N , 2-naphthol (1.73 g, 12 mmol) was dissolved in dry
2
tetrahydropyran (6 mL). To the stirred solution, t-BuLi (18 mL,
Experimental
1
.6 M in pentane) was added dropwise via a syringe at r.t. in ca.
◦
Materials and reagents
12 min, then the solution was stirred for 4 h. At 0 C, to the solution
was added the mixture of DMF (6 mL) and THP (6 mL), then
stirred overnight at room temperature. HCl (5.0%) was added to
adjust the pH to 5 ~ 6. Then the mixture was extracted with ether
Ethyl 2-(2¢-benzothiazolyl) acetate and [Ru(dmb)
prepared according to literature procedure.
3
](PF
Tert-butyllithium
6
) were
2
56,57
(
1.6 M in pentane) and PtCl were purchased from J&K Chemical
2
(
3 ¥ 50 mL). The organic phase was dried over anhydrous Na
The product was purified by column chromatography (silica gel,
CH Cl : hexane = 1 : 1, v/v). Yellow powder was obtained, 0.20 g,
yield: 9.7%. M.p. 84.7–85.9 C. H NMR (400 MHz, CDCl
2
SO
4
.
Ltd. Other chemicals are analytical pure and were used as received
without further purification. Solvents were dried and distilled for
synthesis or spectroscopic studies.
2
2
◦
1
3
): d
0.32 (s, 1H), 10.10 (s, 1H), 8.16 (s, 1H), 7.89 (d, J = 8.0 Hz, 1H),
.73 (d, J = 8.4 Hz, 1H), 7.57 (t, J = 8.0 Hz, 1H), 7.36 (t, J = 7.6
1
7
Apparatus
Hz, 1H), 7.29 (s, 1H). TOF-HRMS m/z: calcd for C11
H] ) 171.0446, found 171.0441.
H
7
O ([M -
2
NMR spectra were recorded on a 400 MHz Varian Unity Inova
spectrophotometer. Mass spectra were recorded with Q-TOF
Micro spectrometer and MALDI micro MX. UV-Vis absorption
spectra were recorded on a HP8453 UV-visible spectrophotometer.
Fluorescence spectra were recorded on a JASCO FP-6500 or
a Sanco 970 CRT spectrofluorometer. Luminescent lifetimes
were measured on Horiba Jobin Yvon Fluoro Max-4 (TCSPC).
Elemental analysis was performed with vario EL III. The melting
points were measured with X-4 Melting-point Apparatus. Flow
cell coupled to a fluorospectrometer was used in the luminescent
-
Synthesis of L-4. Under N , 3-hydroxy-2-naphthaldehyde
2
(100.0 mg, 0.58 mmol) was dissolved in anhydrous methanol
(9 mL). 2-(2¢-benzothiazolyl) acetate (128.6 mg, 0.13 mmol) and
3 mL (0.03 mmol) of piperidine were added, and the solution was
refluxed. Precipitate appeared after 0.5 h; the solution was refluxed
for 4 h. After cooling to r.t., water (10 mL) was added and the
mixture stirred for 15 min. Precipitate was collected with filtration,
washed with water and cold methanol (10 mL), and dried under
vacuum. An orange solid was obtained, 0.13 g, yield: 70.1%. M.p.:
35
2
O sensing.
◦
1
2
(
88.6–299.3 C. H NMR (400 MHz, CDCl
s, 1H), 8.10 (d, J = 8.0 Hz, 1H), 7.97 (d, J = 8.0 Hz, 2H), 7.89 (d,
J = 8.4 Hz, 2H), 7.80 (s, 1H), 7.62 (t, J = 7.6 Hz, 1H), 7.56–7.51 (m,
3
): d 9.18 (s, 1H), 8.24
Synthesis of L-3. Under N
2
, salicylaldehyde (580.0 mg,
4
.75 mmol) was dissolved in anhydrous methanol (70 mL). 2-(2¢-
benzothiazolyl) acetate (1.05 g, 4.75 mmol) and 24 mL (0.24 mmol)
of piperidine were added, and the solution was heated to reflux.
Precipitate appeared after 15 min. The mixture was refluxed for
a further 5 h. After cooling to room temperature, water (15 mL)
was added and the mixture was stirred for 15 min. The precipitate
was collected, washed with water and cold methanol (10 mL), then
dried under vacuum. A yellow solid was obtained, 1.12 g, yield:
1
3
2
1
1
H), 7.43 (t, J = 8.0 Hz, 1H). C NMR (100 M Hz, CDCl ) d 160.1,
52.7, 150.0, 141.6, 137.2, 135.5, 130.7, 130.6, 129.3, 129.0, 127.9,
26.73, 126.4, 125.7, 123.2, 121.9, 120.9, 119.1, 113.0. ES-HRMS
m/z: calcd for C20
3
+
H
12NO
2
S ([M] ) 330.0589, found 330.0592.
Synthesis of Pt-4. Under N
dissolved in 1 mL of benzonitrile by heating at 160 C for several
2
, PtCl
2
(103.0 mg, 0.39 mmol) was
◦
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minutes. L-4 (80.0 mg, 0.24 mmol) in 2-ethoxyethanol (6 mL)
and benzonitrile (3 mL) was added via syringe. The mixture was
stirred for 1 h at 140 C. The solution was cooled. 353 mL of
coumarin ligand (L-4) of Pt-4, instead of using the commercially
available 2-hydroxyl-1-naphthalaldehyde, to avoid steric hindrance
of the cyclometallation. The coumarin ligands were treated with
◦
Hacac and 462 mL of triethylamine were added and the solution
was stirred overnight at r.t. Then 10 mL of hexane was added and
the precipitate was collected with filtration. The crude product was
PtCl and then with Hacac. The compounds were obtained with
2
moderate to satisfying yields (Scheme 1). Complexes Pt-1 and Pt-2
9
were prepared for comparison.
washed with CH
2
Cl
2
and hexane. An orange solid was obtained,
◦
1
4
9
7
0.3 mg, 27.0%. M.p. > 300 C. H NMR (400 MHz, CDCl
.81 (s, 1H), 8.96 (d, J = 7.6 Hz, 1H), 7.76–7.70 (m, 3H), 7.51–
.52 (m, 2H), 7.42–7.37 (m, 2H), 7.33 (t, J = 8.0 Hz, 1H), 5.57
3
): d
UV-vis absorption/emission spectra of the ligands and the
complexes
Ligand L-1 shows absorption in UV region (290 nm). Conversely,
the ligands with coumarin subunit show absorption in visible
range. For example, L-2 shows intense absorption at 464 nm (e =
(
s, 1H), 2.02 (s, 3H), 1.99 (s, 3H). MALDI-HRMS m/z: calcd
+
for C25
Calcd. For C25
.15; Found: C, 46.83; H, 3.16; N, 2.06.
H
17NO
4
NaSPt ([M+Na] ) 645.0424, found 645.0375. Anal.
H
17NO
4
PtS (0.33 CH Cl ): C, 46.76; H, 2.74; N,
2
2
-
1
-1
50600 M cm ). Interestingly, the coumarin ligand with large p-
2
conjugation (L-4) does not show red-shifted absorption compared
to L-2. The red-shifted absorption of L-2 may be due to the more
significant intramolecular charge transfer (ICT) feature of the
ligand.
Computational Methods. All calculations were performed us-
59
ing Gaussian 09 W (Gaussian, Inc.). The gas phase geometry
optimizations were calculated using B3LYP functional with the
6
-31G(d) basis set. The excitation energy was calculated with the
Compared to the absorption of ligands, the Pt(II) complexes
generally show bathochromically shifted absorptions (Fig. 1b).
The absorption of the complexes in the visible region are due to
time-dependent DFT (TDDFT) method based on the optimized
singlet ground state geometry. The spin-density of the triplet state
was calculated with the energy minimized T
1
1
1,9
1
state geometries.
the S → MLCT/ IL transitions. Absorption bands of the ligand
0
p–p transition are at ca. 380 nm. Pt-2 shows intense absorption
Upconversions. Diode pumped solid state laser was used
-
1
-1
at 496 nm (e = 47800 M cm ). This significant light-harvesting
as the excitation source for the upconversions. The sam-
ples were purged with N or Ar for 15 min before mea-
ability is ideal for applications.
2
surement. The upconversion quantum yields were determined
with a laser dye 4-dicyanomethylene-6-(p-dimethylaminostyryl)-
2
0
-methyl-4H-pyran (DCM) as the quantum yield standard (U =
.10 in CH Cl ) and the quantum yields were calculated with
2
2
41
eqn (1), where Uunk, Aunk, Iunk and hunk represents the quantum
yield, absorbance, integrated photoluminescence intensity and
the refractive index of the samples. The photography of the
upconversion were taken with Sumsang NV 5 digital camera. The
exposure times are the default values of the camera.
2
⎛
⎜
⎝
⎞⎛
⎟⎜
⎟⎜
⎟⎜
⎞⎛
⎟⎜
⎟⎜
⎟⎜
⎞
⎟
⎟
⎟
Astd
Iunk
hunk
Φunk = 2Φ ⎜
(1)
std
⎜
⎜
Aunk ⎟⎜ I ⎟⎜ h
⎟
⎠⎝ std ⎠⎝ std
⎠
Results and discussions
Design and synthesis of the complexes
Pt-1 and Pt-2 were reported to show high phosphorescence
9
quantum yields. Pt-2 shows exceptionally long phosphorescence
9
lifetime (27.9 ms). However, the diversity of the complex structure
with directly cyclometallated fluorophore is very limited. Thus,
Pt-3 with coumarin subunit is designed, in which the coumarin
subunit is without the electron-donating diethylamino group
Fig. 1 UV-vis absorption spectra of (a) the ligands and (b) the Pt(II)
-5
◦
(
Scheme 1). We also designed a complex containing coumarin
complexes. In CH Cl (c = 1.0 ¥ 10 M; 25 C).
2
2
with larger p-conjugated scaffold (Pt-4, Scheme 1). Thus we can
reveal the relationbetween the molecular structure ofthe coumarin
chromophore and the phosphorescence property of the complexes.
The synthesis of the ligands followed the routine procedure
The emission maxima of the ligands are dependent on the
p-conjugation and the ICT character of the ligands (Fig. 2a).
For example, L-4 with large p-conjugation shows the red-shifted
emission than L-3. However, L-2 shows red-shifted emission at
497 nm compared to L-3 and L-4. This result indicates that
the fluorescence emission of the ligands is mainly dependent on
the ICT feature fluorophore (Table 1). For example, L-2 shows
quantum yield up to 0.613, conversely L-3 and L-4 show much
lower quantum yield of 0.175% and 0.026%, respectively.
(
Scheme 1). The o-aminothiophenol and ethyl cyanoacetate were
used to prepare the ethyl 2-(2¢-benzothiazolyl) acetate. The ligand
for cyclometallation was synthesized through the piperidine-
catalyzed Knoevenagel condensation with substituted o-hydroxy
aldehydes and ethyl 2-(2¢-benzothiazolyl) acetate under mild
conditions. 2-hydroxyl-3-naphthalaldehyde is used for synthesis of
5
956 | Dalton Trans., 2011, 40, 5953–5963
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Table 1 Photophysical parameters of platinum complexes Pt-1–Pt-4 and the ligands L-1–L-4 (the data of the known complexes Pt-1 and Pt-2 are
presented for comparison)
a
b
c
d
-1 e
k
nr (s-1)e
l
abs (nm)
l
ex (nm)
l
em (nm)
U
f
U
p
t (ns)
k
r
(s )
h
6
8
8
7
6
4
4
3
9
L-1
299 (1.77)
448 (5.03), 464 (5.06)
364 (3.76)
289 (0.17), 300 (0.14), 376 (0.37)
256 (2.31), 316 (1.80), 331 (1.63), 385 (0.76)
302 (1.31), 389 (2.18), 469 (3.84), 496 (4.78)
281 (1.61), 346 (1.21), 364 (1.42), 404 (1.18), 443 (0.69), 472 (0.50) 476
259 (3.66), 301 (1.99), 370 (2.11), 414 (1.55), 455 (1.21), 487 (0.86) 472
313
475
389
402
404
476
363
497
452
475
543, 585
596, 646
597, 650
629, 686
0.009
0.613
0.175
0.026
—
—
—
—
0.91 ns
2.52 ns
1.21 ns
2.39 ns
0.34 ms
20.3 ms
1.59 ms
1.28 ms
9.9 ¥ 10
2.4 ¥ 10
1.4 ¥ 10
1.1 ¥ 10
1.1 ¥ 10
1.8 ¥ 10
1.9 ¥ 10
9.6 ¥ 10
1.1 ¥ 108
1.5 ¥ 10
h
h
h
L-2
8
L-3
L-4
Pt-1
Pt-2
Pt-3
Pt-4
6.8 ¥ 10
8
4.1 ¥ 10
h
6
—
—
—
0.36
0.37
0.03
0.01
1.87 ¥ 10
h
f
g
4
3.0 ¥ 10
h
5
3.8 ¥ 10
h
5
—
7.7 ¥ 10
a
4
-1
-1
b
c
Extinction coefficients (10 M cm ) are shown in parentheses. Asterisks indicate emission peaks appearing as shoulders or weak bands. Quantum
d
e
yield of fluorescence in CH
rate constant (knr). k
2
Cl
2
.
Quantum yield of phosphorescence in CH
2
Cl
2
. radiative deactivation rate constant (k
r
) and non-radiative deactivation
1
1
3
3
r
= fem/tem; knr = 1/tem(1 - Uem). It is assumed that the emitting excited state is produced vis MLCT/ IL→ MLCT/ IL with unit
f
5
g
5 h
efficiency. literature value is 0.25 ms in 2-methyltetrahydrofuran solutions. literature value is 27.9 ms, in 2-methyltetrahydrofuran. Not applicable.
Pt-3). Interestingly, ligand L-4 emits at shorter wavelength than
L-2 (Fig. 2a).
The efficiency of the light-harvesting of coumarin-containing
1
complexes is dependent on the relative energy levels of the IL state
1
52,60,63
of the ligand and the MLCT state of the complex.
In order
to study the light-harvesting effect of the coumarin-containing
complexes, the excitation spectra of the complexes were also
studied and were compared with the UV-vis absorption spectra
of the complexes (ESI†). We found that the excitation spectra
of the complexes are superimposable to the UV-vis absorption,
1
1
which indicate efficient energy transfer between IL/ MLCT state
3
63
and the MLCT state.
The photophysical properties of the ligands and complexes were
summarized in Table 1. Notably Pt-1 and Pt-2 show high room
temperature phosphorescence quantum yield, up to 0.362 and
9
0
.371, respectively.
Pt-2 shows the longest luminescent lifetimes among the com-
9
plexes studied (t = 20.3 ms). Without the diethylamino substituent,
Pt-3 and Pt-4 show much shorter luminescent lifetimes (t = 1.59 ms
and 1.28 ms, respectively). We noticed that a cyclometallated Ir(III)
64
complexes with the same coumarin ligand of Pt-2 was reported.
However, that Ir(III) complex show shorter luminescent lifetime
64
(
t = 11.3 ms).
3
IL Triplet excited state: assignment of the emissive excited states
Fig. 2 Normalized emission spectra of (a) the ligands and (b) the com-
plexes. The known complexes Pt-1 and Pt-2 were studied for comparison.
In CH Cl (c = 1.0 ¥ 10 M; 25 C).
2 2
of the cyclometallated complexes with DFT/TDDFT calculations
-5
◦
The electronic structure of the lowest-lying triplet excited states
of the transition metal complexes can be revealed with the DFT
calculations, thus components of the emissive triplet excited states
Room temperature (r.t.) emissions beyond 500 nm were found
for the complexes, especially for Pt-2, which shows emission bands
at 596 nm (Fig. 2b). Pt-4 gives more red-shifted emission at
3
3
( IL or MLCT) can be assigned, and the emission property of the
12–14,35–36,65–72
complexes can be predicted to some extent.
6
29 nm. R.t. phosphorescence in deep-red and near-IR region
Firstly the ground state geometry of Pt-2 was optimized
with DFT calculations. Planar square coordination geometry
was found for the Pt(II) centers (Fig. 3). The coumarin and
acac auxiliary ligands take co-planar geometry. Thus large p-
conjugation was expected for this complex.
The frontier molecular orbitals were examined (Fig. 3).
Coumarin contributes significantly to both the HOMO and
LUMO. The Pt(II) atom contributes only slightly to the HOMO
and LUMO. In order to investigate the UV-Vis absorption, the
singlet excited states of Pt-2 were studied with the TDDFT cal-
culations (Table 2). Large oscillator strength was observed for the
is in particularly interesting because these materials can be
used as emitters for optical fiber communications. The large
Stokes shifts of the emissions, and the significant quenching of
O on the emission support the assignment of the emission as
phosphorescence.
Interestingly, Pt-3 and Pt-2 show the same emission wavelength,
despite the drastically different ICT feature of the ligands, as well
as the different fluorescence emission of the ligands (Fig. 2a). Pt-4,
the complex with the large p-conjugation ligand, however, shows
the most red-shifted emission (by 33 nm compared to Pt-2 and
60
2
1,61,62
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Fig.
4
Frontier molecular orbitals of Pt-4. Calculated at the
Fig.
3 Frontier molecular orbitals of Pt-2. Calculated at the
B3LYP/6-31G((d)/LanL2DZ level using Gaussian 09W.
B3LYP/6-31G((d)/LanL2DZ level using Gaussian 09W.
The singlet excited state of Pt-4 was studied (Table 3). The
S
0
→S
is correlated to the S
experimental results (Fig. 1b). The calculated S
excitation energy of 427 nm, which is close to the absorption at
69 nm (Fig. 1b). Thus the absorption at 427 nm is assigned as
1
transition (f = 0.5457), thus we expect intense absorption
→S transition, which is supported by the
state is with
S
0
→S
1
excitation energy is calculated as 429 nm, with much
0
1
smaller oscillator strength (f = 0.2797), which indicate weak
absorption compared to Pt-2 (for which the f value is larger).
1
The calculated S
0
→T
1
energy gap is 2.02 eV (Table 3), which is
4
much smaller than that of Pt-2. Indeed we observed emission at
629 nm for Pt-4, which is red-shifted by 33 nm compared to Pt-2.
Minor involvement of the Pt(II) is found for the T
the electronic composition of the transition, the T
assigned as IL state.
1
1
IL/ MLCT, based on the distribution of the electron density of
the molecular orbitals (Fig. 3).
1
state. Based on
state can be
The triplet excited states of Pt-2 were also studied with
the TDDFT calculations based on the optimized ground state
1
3
geometry (Table 2). The calculated S
0
→T
1
energy gap is 2.17 eV
We studied the spin density of T state (Fig. 5). The spin density
1
(
572 nm), which is close to the emission wavelength at 596 nm
contours of the complexes are localized on the thiazo ligands. The
Pt(II) ions contribute to the spin density. For the acac ligands,
however, no contribution was found. This result indicates that the
3
(
Fig. 2b). The T
1
state can be assigned as IL state, mixed with
3
MLCT feature. Thus the long phosphorescence lifetime of Pt-2
3
Ÿ
may be due to the IL T
Pt-1 was also studied with DFT/TDDFT calculations (ESI†).
The calculated S energy gap is 505 nm, which is close to the
experimental emission at 543 nm (Fig. 2b). However, we found
significant contribution of the Pt(II) ion to the HOMO and LUMO
of Pt-1. Thus we expect Pt-1 will show shorter phosphorescence
1
state.
triplet state are independent on the acac ligands, and it is the C N
cyclometalation ligands that dictate the photophysical properties
5,45
0
→T
1
of the complexes.
73
Enhanced phosphorescent O
2
sensing
35
lifetime than that of Pt-2.
Luminescent O
2
sensing is based the quantitative relation between
The singlet excited states of Pt-4 were also studied with
DFT/TDDFT calculations. The geometry of the Pt-4 was op-
timized and the frontier molecular orbitals were presented in Fig.
the quenched phosphorescence of transition metal complexes
61,62,74
and the O
luminescent O
is more sensitive O
Ru(II) polypyridine complexes or Pt(II) porphyrin complexes were
2
partial pressure,
We have been interested in
3
2
sensing and we found that the long-lived IL state
3
14,35,75
4
. The HOMO and LUMO orbitals are localized on coumarin
2
sensing than the MLCT state.
Usually
ligand with minor contribution from Pt(II).
Table 2 Electronic excitation energies (ev) and corresponding oscillator strengths (f ), main configurations and CI coefficients of the low-lying
electronically excited states of complex Pt-2, calculated by TDDFT, based on the ground state geometries
TDDFT//B3LYP/6-31G(d)
a
b
c
d
e
Electronic transition
Energy
f
Composition
CI
Character
Singlet
S
S
0
0
→S
→S
1
3
2.90 eV 427 nm
3.38 eV 353 nm
0.5457
0.1753
H–2→L
H→L
0.1461
0.6257
0.1077
0.1467
0.6266
0.1208
0.1170
0.1242
0.6182
0.1873
0.1120
0.1206
0.7351
LLCT & MLCT
IL
H–6→L
H–2→L
H–1→L
H→L
LLCT & MLCT
IL & LLCT
IL
H→L+1
H–6→L
H–2→L
H–1→L
H→L
LLCT
S
S
0
0
→S
5
3.60 eV 345 nm
0.1365
LLCT & MLCT
IL & LLCT
IL
LLCT & MLCT
IL
f
Triplet
→T
1
2.17 eV 572 nm
0.0000
H–2→L
H→L
a
b
c
Only the selected low-lying excited states are presented. Oscillator strength. H stands for HOMO and L stands for LUMO. Only the main configurations
d
e
are presented. The CI coefficients are in absolute values. IL: intraligand, LLCT: ligand-to-ligand charge transfer, MLCT: metal-to-ligand charge transfer.
f
No spin-orbital coupling effect was considered, thus the f values are zero.
5
958 | Dalton Trans., 2011, 40, 5953–5963
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Table 3 Electronic excitation energies (eV) and corresponding oscillator strengths (f ), main configurations and CI coefficients of the low-lying
electronically excited states of complex Pt-4, calculated by TDDFT based on the optimized ground state geometries
TDDFT//B3LYP/6-31G(d)
a
b
c
d
e
Electronic transition
Energy
f
Composition
CI
Character
Singlet
S
0
→S
1
2.89 eV 429 nm
0.2797
H–2→L
H→L
0.1261
0.6232
0.6636
0.1153
0.6396
0.1232
0.5036
0.3527
0.1738
0.7411
0.1328
LLCT
IL
LLCT
S
S
0
0
→S
→S
3
5
3.29 eV 376 nm
3.65 eV 340 nm
0.1294
0.1920
H–2→L
H–6→L
H–3→L
H–9→L
H–6→L
H→L+2
H–1→L+2
H→L
LLCT
S
0
0
→S15
4.21 eV 294 nm
0.1418
IL
f
Triplet
S
→T
1
2.02 eV 615 nm
0.0000
IL & MLCT
IL
IL
H→L+2
a
b
c
Only the selected low-lying excited states are presented. Oscillator strength. H stands for HOMO and L stands for LUMO. Only the main configurations
d
e
are presented. The CI coefficients are in absolute values. IL: intraligand, LLCT: ligand-to-ligand charge transfer, MLCT: metal-to-ligand charge transfer.
f
No spin-orbital coupling effect was considered, thus the f values are zero.
quenched by 98.9% in air, compared to 73.6% for Pt-3. Pt-4 shows
lower O
In order to quantitatively compare the O
of the complexes, the O sensing in polymer films were studied
Fig. 7). Pt-4 was not studied in the film due to its poor emission
2
sensitivity than Pt-2 (ESI†).
2
sensing property
2
(
property. Two type of sensing experiments were carried out, i.e. the
phosphorescence response of the films toward the switch between
N
2
and O
films toward step variation of the O
d). The response time t 95 and recovery time t
2
(Fig. 7a, b), and the dynamic response of the sensing
partial pressure (Fig. 8c,
95 were used to
2
↓
↑
characterize the response dynamics. Fast response (0.6 s) and
recovery (0.9 s) were observed for the sensing films. For Pt-1,
we found the quenching of the phosphorescence is not significant,
Fig. 5 Spin density surfaces of the T
Pt-4. Based on the optimized triplet state geometry.
1
excited state of Pt-1, Pt-2, Pt-3 and
6
1,62,64
e.g. the emission is quenched by 23.9% in neat O
however, the sensitivity is much higher, e.g. the emission intensity
is quenched by 91.3% in O (Fig. 7a). Pt-3 shows much lower
2
(ESI†). For Pt-2,
used for the O
little O sensing has been performed with cyclometallated Pt(II)
complexes. Thus the O
studied in detail. For Pt-2, the intense absorption in visible region
(
2
2
sensing.
However, to the best of knowledge,
2
1
,46
2
2
sensing properties of the complexes were
sensitivity for oxygen sensing (Fig. 7b).
-
1
-1
e = 47800 M cm at 496 nm), long phosphorescence lifetime (t =
0.3 ms) and the high phosphorescence quantum yield (0.371) are
ideal for application for O sensing. Firstly the O sensitivities of
2
2
the complexes were studied in solution (Fig. 6 and ESI†). For Pt-1,
the phosphorescence was quenched by 89.2% in air compared to
that in N
2
. The emission is almost completely quenched in neat
O
2
. For Pt-2, however, the emission in air is almost completely
quenched (Fig. 6a), For Pt-3, however, the quenching effect is
lower than that of Pt-2. For example, the emission of Pt-2 is
Fig. 6 Emission spectra of (a) Pt-2, lex = 476 nm, and (b) Pt-3, lex
=
Fig. 7 Phosphorescence response of the complexes to step variations of
4
76 nm. In CH Cl solution saturated with air, oxygen and nitrogen,
2
2
O
2
concentration. (a) and (c) Pt-2, lex = 476 nm, lem = 650 nm. (b) and (d)
-5
◦
◦
respectively. c = 1.0 ¥ 10 M, 25 C.
Pt-3. lex = 476 nm, lem = 596 nm. 25 C.
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Table 4 Parameters of O
2
sensing film of complex Pt-1, Pt-2 and Pt-3
with IMPEK-C as supporting matrix (fitting result of the two site model)
a
a
b
b
app c
d
f
1
f
2
K
SV1
K
SV2
K
SV
pO
2
Pt-1
Pt-2
Pt-3
0.7503
0.9146
0.8781
0.2497
0.0854
0.1219
0.0001
0.0282
0.0000
0.0073
0.0004
0.0024
0.00190
0.02583
0.00029
526.9
38.7
3418.1
a
b
Ratio of the two portions of dyes. Quenching constants of the two
c
app
d
1 2 SV2
portions. Weighted quenching constant, KSV = f KSV1 + f K . The
oxygen partial pressure at which the initial emission intensity of the film is
quenched by 50% and calculated as 1/KSV. In Torr.
Fig. 8 Two-sites model plots for sensing film of Pt-1, Pt-2 and Pt-3 in
IMPEK-C. Intensity ratios I /I vs. O partial pressure (Torr).
3
3
1
0
2
Acceptor* + Acceptor*→ Acceptor* + Acceptor (TTA)
The response of the films toward small step of O partial
2
pressure variation was also studied (Fig. 7c, d). The response
of Pt-1, Pt-3 are small (Fig. 7b and ESI†) but the response of
Pt-2 is more significant (Fig. 7c). The phosphorescence of the
sensing films are fully reversible, i.e. the emission intensity is
fully recovered even after long time of continuous irradiation,
indicating good photostability of the complexes, which is ideal for
1
Acceptor * → Acceptor + hv (emission of fluorescence)
This modular upconversion is in particular promising for
applications because the excitation and emission wavelength can
be tuned by independent selection of the sensitizer and the
annihilator (see ESI for the Jablonski diagram which demonstrates
40–44
61,62
the photophysical processes†).
O
2
sensing applications.
Significant photobleaching (photo-
However, the present understanding of the photophysics in-
volved in TTA based upconversion is still premature. Little
is known on the effect of the excited state lifetimes on the
upconversion efficiency. It is important to use complexes with
intense visible-light absorption capability and long-lived triplet
excited states for the TTA based upconversion, but the related
reports are rare.
decomposition) was observed for a previously reported Ir(III)
complex (the UV-vis absorbance decreased by ca. 80% within
6
4
2
0 min of irradiation). For Pt-2, no photobleaching was observed
even with 30 min continuous irradiation (Fig. 7).
sensing with the polymer films (a heterogeneous system)
79
O
2
61,62,76,77
can be described by the two-site model.
dye molecules are considered to be distributed in two different
microenvironments in the polymer film, which are defined as f
and f , respectively (f + f = 1), each portion is with different
accessibility, i.e. the two portions show different quenching
constants (KSV1 and KSV2, eqn (2)).
In this model, the
Firstly, the emission spectra of the complexes with 473 nm laser
excitation were studied (Fig. 9a). Only Pt-2 gives intense emission.
Weak emission was observed for other complexes, which is due
to either the poor absorption in the 473 nm region (Pt-1) or low
1
2
1
2
O
2
2
+
phosphorescence quantum yield (Pt-3, Pt-4 and [Ru(dmb) ] ).
3
2
+
I0
I
1
[Ru(dmb)3] gives very weak emission, which is one ninth of Pt-2
=
f
f
(2)
(Fig. 9a).
1
2
+
1
+ KSV 1pO2 1+ KSV 2pO2
The O
Fig. 8). The quenching constants obtained from the fitting were
listed in Table 4. The quenching constant of Pt-2 is 13.6-fold of
that Pt-1. We compared the O sensing of Pt-2 with a recently
reported cyclometalated Ir(III) complexes (with triphenylamine
2
sensing data (Fig. 7 and ESI†) were fitted with eqn (2)
(
2
46
caped 2-phenylpyridine ligand). The KSV of Pt-2 is 7.4-fold of
the triphenylamine capped cyclometalated Ir(III) complexes. We
noticed that a cyclometallated Ir(III) complexes with the coumarin
64
2+
ligand was used for O
show much shorter phosphorescence lifetime (11.3 ms) than Pt-2.
The O sensitivity of Pt-2 is ca. 8.0-fold of the Ir(III) complex (for
which Ksv = 0.0032 Torr ).
2
sensing. However, that Ir(III) complex
Fig. 9 (a) Emission of Pt-1, Pt-2, Pt-3, Pt-4 and [Ru(dmb)3] (1.0 ¥
-5
10 M) with excitation by 473 nm laser (5 mW). (b) Emission of
the upconverted fluorescence of 9,10-diphenylanthracene (DPA, 4.3 ¥
10 M) and the residual photoluminescence of Pt-1, Pt-2, Pt-3, Pt-4
3 6 2
and [Ru(dmb) ][PF ] (1.0 ¥ 10 M) in the upconversion experiments.
2
-5
-
1
64
-5
Excitation by 473 nm laser (5 mW). The asterisks denote the scattered
laser at 473 nm. 25 C.
Enhanced triplet–triplet-annihilation based upconversion
◦
Triplet–triplet-annihilation (TTA) based upconversion has at-
78–80
Next, 9,10-diphenylanthracene (DPA) was added into the
solution of the complexes and the emission of the mixtures upon
473 nm laser excitation were studied (Fig. 9b). The phosphores-
cence of Pt-2 was quenched in the presence of DPA. Concurrently,
the characteristic blue fluorescence emission of DPA was observed
tracted much attention (eqn (3)),
and is believed to be
promising for practical applications, such as to improve the
78,81
efficiency of dye-sensitized solar cells.
3
3
Sensitizer* + Acceptor → Sensitizer + Acceptor* (TTET) (3)
960 | Dalton Trans., 2011, 40, 5953–5963
5
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Table 5 Luminescence lifetimes (t), Stern–Volmer quenching constants
in visible region (Fig. 1b) and the longest triplet excited lifetime
among the complexes studied (20.3 ms, Table 1). An upconversion
quantum yield of 15.4% was observed. This high efficiency
exceeds the theoretical maximum of 11.1% and is among highest
values ever reported. Recently it was proposed that molecular
encounters with spin manifold other than triplet is also effective
(
K
SV) and bimolecular quenching constants (k
q
) of the Pt-2, Pt-3, Pt-4 and
2+
◦
[
Ru(dmb)
3
]
complexes. In deaerated CH
2
Cl
2
. 25 C
3
-1
/10 M s-1
9
-1
t/ms
K
sv/10 M
k
q
UUC/%
Pt-2
Pt-3
Pt-4
20.3
1.59
1.28
0.84
133.46
8.22
8.20
6.57
5.17
6.40
4.68
15.4
5.3
2.8
1.2
42
for the upconverted fluorescence. Herein Pt-2 is an example
2+
that upconversion quantum efficiency higher than the theoretical
maximum can be achieved. The high upconversion quantum yield
of Pt-2 is due to its intense absorption and its long-lived triplet
state.
[
Ru(dmb)
3
]
3.93
(
Fig. 9b). For [Ru(dmb)
3
][PF ] , however, the phosphorescence is
6
2
not quenched and no significant upconverted fluorescence was
observed (Fig. 9b). Irradiation of DPA alone at 473 nm does not
produce any emission. Little upconverted emissions were observed
with Pt-1, Pt-3 and Pt-4.
It should be pointed out that upconversion is dependent on the
experimental conditions, such as sensitizer/acceptor concentra-
tions, excitation power and excitation wavelength, etc. However,
our results show that the upconversion threshold for Pt-2 is much
lower than that of other complexes.
The emission of the complexes alone and the upconversion with
4
73 nm laser excitation were visible with the unaided eye (Fig. 11).
For the complexes alone (Fig. 11a), the phosphorescences were
observed with 473 nm laser excitation. Pt-2 gives the strongest
emission (saturation was observed for the digital photography).
Pt-4 shows the weakest emission but with deep-red color (the
longest emission wavelength, Fig. 2b). With addition of the
annihilator/acceptor into the solution, the upconverted blue
fluorescence of DPA were observed for Pt-2, Pt-3 and Pt-4, among
which Pt-2 shows the most intense blue emission (Fig. 11b).
The concentration of the DPA in our upconversion is much
-
4
43,44,79,82
lower than that in literatures (10 M-0.1 M).
The low-
threshold of the upconversion with Pt-2 demonstrated the signifi-
3
cant effect of light-harvesting and the long-lived IL triplet excited
state of the sensitizer on the upconversion. Upconversion with
5
32 nm laser excitation was also investigated and similar results
were observed (ESI†).
The key step for TTA upconversion is TTET (see the Jablonski
diagram in ESI†). In order to study the TTET quantitatively, the
quenching effect of DPA on the phosphorescence of sensitizers
were studied and the Stern–Volmer quenching curves were con-
61,62,79
structed (Fig. 10).
Fig. 10 Stern–Volmer plots generated from intensity quenching of
Fig. 11 The photographs of (a) the emission of the complexes alone and
(b) the upconversion, i.e. emission of the mixed solution of sensitizers and
2+
3
complex [Ru(dmb) ] , Pt-2, Pt-3, Pt-4 photoluminescence measured as
a function of DPA concentration in CH
complexes are 1.0 ¥ 10 mol dm . lex = 473 nm. 25 C.
2
Cl
2
. The concentrations of all the
3 2
DPA. 473 nm laser excitation (5 mW). In deaerated CH Cl . c[sensitizers] =
1.0 ¥ 10 M. c[DPA] = 4.3 ¥ 10 M. 25 C.
-5
-3
◦
-5
-5
◦
5
-1
Stern–Volmer quenching constant KSV = 1.33 ¥ 10 M was
observed for Pt-2, which is at least of 33-fold of [Ru(dmb) ][PF
SV = 3.93 ¥ 10 M ), a benchmark triplet sensitizer for
TTA upconversion. This is due to the longer T state lifetime
and the significant light-harvesting effect of Pt-2 than that of
Ru(dmb) ][PF . The Stern–Volmer constant of Pt-2 is also much
3
]
6 2
Conclusions
3
-1
(
K
1
We have studied the phosphorescence of cyclometallated Pt(II)
complexes that with the thiazo-coumarin ligand directly cyclomet-
allated. Room temperature phosphorescences were observed for
all the complexes. The emission wavelength of the complexes are
dependent on the extent of the p-conjugation of the ligands, but the
fluorescence emission of the ligands is more sensitive to the ICT
feature of the ligands. The emissive excited state of the complexes
[
3
]
6 2
higher than Pt-3 and Pt-4 (Table 5).
The upconversion quantum yields were determined. The model
complex [Ru(dmb)
3
][PF
6
2
] shows a low quantum yield of 1.2%. For
Pt-3 and Pt-4, higher quantum efficiency of 5.3% and 2.8% were
observed, respectively. Complex Pt-2 shows intense absorption
3
were assigned as IL triplet excited state with DFT/TDDFT
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calculations. The complexes were used for luminescent O
ing and triplet–triplet-annihilation based upconversion. The O
2
sens-
23 F. Hua, S. Kinayyigit, J. R. Cable and F. N. Castellano, Inorg. Chem.,
2
006, 45, 4304.
2
2
4 C. Ed Whittle, J. A. Weinstein, M. W. George and K. S. Schanze, Inorg.
Chem., 2001, 40, 4053.
sensitivity of the Pt-2 sensing film is 8.0-fold of a recently reported
cyclometallated Ir(III) complex. The TTET efficiency of Pt-2 in
25 I. E. Pomestchenko, C. R. Luman, M. Hissler, R. Ziessel and F. N.
5
-1
9
-1
-1
upconversion (KSV = 1.33 ¥ 10 M , k
DPA as quencher) is 33-fold of [Ru(dmb)
q
= 6.57 ¥ 10 M s .
][PF , a benchmark
Castellano, Inorg. Chem., 2003, 42, 1394.
2
2
2
2
6 T. J. Wadas, R. J. Lachicotte and R. Eisenberg, Inorg. Chem., 2003, 42,
3
]
6 2
3
772.
triplet sensitizer for TTA based upconversion. The upconversion
quantum yield of Pt-2/DPA is up to 15.4%. We propose that
the complexes with intense absorption in visible region and long-
7 S. Goeb, A. A. Rachford and F. N. Castellano, Chem. Commun., 2008,
814.
8 J. B. Seneclauze, P. Retailleau and R. Ziessel, New J. Chem., 2007, 31,
1412.
9 M. Hissler, W. B. Connick, D. K. Geiger, J. E. McGarrah, D.
Lipa, R. J. Lachicotte and R. Eisenberg, Inorg. Chem., 2000, 39,
447.
3
lived emissive IL excited states can be accessed with direct
cyclometallation of the organic fluorophores; this approach will
be useful for design of new phosphorescent transition metal
3
3
0 I. V. Sazanovich, M. A. H. Alamiry, J. Best, R. D. Bennett, O. V.
Bouganov, E. S. Davies, V. P. Grivin, A. J. H. M. Meijer, V. F. Plyusnin,
K. L. Ronayne, A. H. Shelton, S. A. Tikhomirov, M. Towrie and J. A.
Weinstein, Inorg. Chem., 2008, 47, 10432.
complexes and for their applications in luminescent O sensing,
2
photocatalysis, triplet–triplet-annihilation based upconversion,
etc.
1 A. A. Rachford, S. Goeb and F. N. Castellano, J. Am. Chem. Soc., 2008,
1
30, 2766.
Acknowledgements
32 X. Han, L. Wu, G. Si, J. Pan, Q. Yang, L. Zhang and C. Tung, Chem.–
Eur. J., 2007, 13, 1231.
We thank the NSFC (20972024 and 21073028), the Fundamental
Research Funds for the Central Universities (DUT10ZD212),
Ministry of Education (SRFDP-200801410004 and NCET-08-
33 S. Suzuki, R. Sugimura, M. Kozaki, K. Keyaki, K. Nozaki, N. Ikeda,
K. Akiyama and K. Okada, J. Am. Chem. Soc., 2009, 131, 10374.
3
3
3
3
3
4 J. E. McGarrah, Y. Kim, M. Hissler and R. Eisenberg, Inorg. Chem.,
2
001, 40, 4510.
0
077), the Royal Society (UK) and NSFC (China-UK Cost-Share
5 S. Ji, W. Wu, W. Wu, P. Song, K. Han, Z. Wang, S. Liu, H. Guo and J.
Zhao, J. Mater. Chem., 2010, 20, 1953.
6 S. Ji, H. Guo, X. Yuan, X. Li, H. Ding, P. Gao, C. Zhao, W. Wu, W.
Wu and J. Zhao, Org. Lett., 2010, 12, 2876.
7 L. Xiong, Q. Zhao, H. Chen, Y. Wu, Z. Dong, Z. Zhou and F. Li, Inorg.
Chem., 2010, 49, 6402.
8 R. Ziessel, J. Am. Chem. Soc., 1993, 115, 118.
Science Networks, 21011130154) and the Education Department
of Liaoning Province (2009T015) for financial support.
Notes and references
1
2
3
4
J. A. G. Williams, Top. Curr. Chem., 2007, 281, 205.
39 Q. Zhou, W. Lei, J. Chen, C. Li, Y. Hou, X. Wang and B. Zhang,
Chem.–Eur. J., 2010, 16, 3157.
40 R. R. Islangulov, J. Lott, C. Weder and F. N. Castellano, J. Am. Chem.
Soc., 2007, 129, 12652.
41 T. N. Singh-Rachford and F. N. Castellano, Coord. Chem. Rev., 2010,
254, 2560.
42 Y. Yap Cheng, T. Khoury, R. G. C. R. Clady, M. J. Y. Tayebjee, N. J.
Ekins-Daukes, M. J. Crossley and T. W. Schmidt, Phys. Chem. Chem.
Phys., 2010, 12, 66.
43 A. Monguzzi, J. Mezyk, F. Scotognella, R. Tubino and F. Meinardi,
Phys. Rev. B: Condens. Matter Mater. Phys., 2008, 78, 195112.
44 A. Monguzzi, R. Tubino and F. Meinardi, Phys. Rev. B: Condens.
Matter Mater. Phys., 2008, 77, 155122.
45 K. Hanson, A. Tamayo, V. V. Diev, M. T. Whited, P. I. Djurovich and
M. E. Thompson, Inorg. Chem., 2010, 49, 6077.
46 C. S. K. Mak, D. Pentlehner, M. Stich, O. S. Wolfbeis, W. K. Chan and
H. Yersin, Chem. Mater., 2009, 21, 2173.
47 F. N. Castellano, I. E. Pomestchenko, E. Shikhova, F. Hua, M. L. Muro
and N. Rajapakse, Coord. Chem. Rev., 2006, 250, 1819.
48 A. A. Rachford, S. Goeb, R. Ziessel and F. N. Castellano, Inorg. Chem.,
2008, 47, 4348.
49 P. Lano e¨ , J. Fillaut, L. Toupet, J. A. G. Williams, H. Le Bozec and V.
Guerchais, Chem. Commun., 2008, 4333.
50 E. O. Danilov, I. E. Pomestchenko, S. Kinayyigit, P. L. Gentili, M.
Hissler, R. Ziessel and F. N. Castellano, J. Phys. Chem. A, 2005, 109,
2465.
51 (a) D. S. Tyson and F. N. Castellano, J. Phys. Chem. A, 1999, 103,
10955; (b) X. Wang, A. D. Guerzo and R. H. Schmehl, J. Photochem.
Photobiol., C, 2004, 5, 55.
52 D. S. Tyson, C. R. Luman, X. Zhou and F. N. Castellano, Inorg. Chem.,
2001, 40, 4063.
53 (a) D. S. Tyson, K. B. Henbest, J. Bialecki and F. N. Castellano, J.
Phys. Chem. A, 2001, 105, 8154; (b) N. D. McClenaghan, Y. Leydet,
B. Maubert, M. T. Indelli and S. Campagna, Coord. Chem. Rev., 2005,
249, 1336.
54 W. Wu, S. Ji, W. Wu, H. Guo, X. Wang, J. Zhao and Z. Wang, Sens.
Actuators, B, 2010, 149, 395.
55 H. Guo, M. L. Muro-Small, S. Ji, J. Zhao and F. N. Castellano, Inorg.
Chem., 2010, 49, 6802.
56 G. Signore, R. Nifos `ı , L. Albertazzi, B. Storti and R. Bizzarri, J. Am.
Chem. Soc., 2010, 132, 1276.
W. Y. Wong and C. L. Ho, Coord. Chem. Rev., 2009, 253, 1709.
Paul I. P. Elliott, Annu. Rep. Prog. Chem., Sect. A, 2010, 106, 526.
P.-H. Lan o¨ e, H. Le Bozec, J. A. G. Williams, J.-L. Fillaut and V.
Guerchais, Dalton Trans., 2010, 39, 707.
5
6
7
8
9
P. I. Djurovich, D. Murphy, M. E. Thompson, B. Hernandez, R. Gao,
P. L. Hunt and M. Selke, Dalton Trans., 2007, 36, 3763.
S.-Y. Chang, Y.-M. Cheng, Y. Chi, Y.-C. Lin, C.-M. Jiang, G.-H. Lee
and P.-T. Chou, Dalton Trans., 2008, 37, 6901.
Z. He, W. Wong, X. Yu, H. Kwok and Z. Lin, Inorg. Chem., 2006, 45,
1
0922.
G. J. Zhou, Q. Wang, W. Y. Wong, D. Ma, L. X. Wang and Z. Y. Lin,
J. Mater. Chem., 2009, 19, 1872.
J. Brooks, Y. Babayan, S. Lamansky, P. I. Djurovich, I. Tsyba, R. Bau
and M. E. Thompson, Inorg. Chem., 2002, 41, 3055.
1
1
0 B. Yin, F. Niemeyer, J. A. G. Williams, J. Jiang, A. Boucekkine, L.
Toupet, H. Le Bozec and V. Guerchais, Inorg. Chem., 2006, 45, 8584.
1 D. N. Kozhevnikov, V. N. Kozhevnikov, M. M. Ustinova, A. Santoro,
D. W. Bruce, B. Koenig, R. Czerwieniec, T. Fischer, M. Zabel and H.
Yersin, Inorg. Chem., 2009, 48, 4179.
2 W. Wu, C. Cheng, W. Wu, H. Guo, S. Ji, P. Song, K. Han, J. Zhao, X.
Zhang, Y. Wu and G. Du, Eur. J. Inorg. Chem., 2010, 29, 4683.
3 W. Wu, W. Wu, S. Ji, H. Guo and J. Zhao, Eur. J. Inorg. Chem., 2010,
1
1
1
1
1
1
1
2
8, 4470.
4 W. Wu, W. Wu, S. Ji, H. Guo, P. Song, K. Han, L. Chi, J. Shao and J.
Zhao, J. Mater. Chem., 2010, 20, 9775.
5 W. Wu, W. Wu, S. Ji, H. Guo, X. Wang and J. Zhao, Dyes Pigm., 2010,
8
9, 199.
6 B. Ma, P. I. Djurovich and M. E. Thompson, Coord. Chem. Rev., 2005,
49, 1501.
7 S. Chan, M. C. W. Chan, Y. Wang, C. Che, K. Cheung and N. Zhu,
Chem.–Eur. J., 2001, 7, 4180.
8 Q. Yang, L. Wu, Z. Wu, L. Zhang and C. Tung, Inorg. Chem., 2002, 41,
2
5
653.
1
2
9 J. E. McGarrah and R. Eisenberg, Inorg. Chem., 2003, 42, 4355.
0 F. Hua, S. Kinayyigit, J. R. Cable and F. N. Castellano, Inorg. Chem.,
2
005, 44, 471.
2
2
1 C. Monnereau, J. Gomez, E. Blart, F. Odobel, S. Wallin, A. Fallberg
and L. Hammarstr o¨ m, Inorg. Chem., 2005, 44, 4806.
2 S. Chakraborty, T. J. Wadas, H. Hester, C. Flaschenreim, R. Schmehl
and R. Eisenberg, Inorg. Chem., 2005, 44, 6284.
5
962 | Dalton Trans., 2011, 40, 5953–5963
This journal is © The Royal Society of Chemistry 2011

View Article Online
5
5
5
6
6
6
7 S. A. McFarland, F. S. Lee, K. A. W. Y. Cheng, F. L. Cozens and N. P.
Schepp, J. Am. Chem. Soc., 2005, 127, 7065.
71 X. Zhang, L. Chi, S. Ji, Y. Wu, P. Song, K. Han, H. Guo, T. D. James
and J. Zhao, J. Am. Chem. Soc., 2009, 131, 17452.
72 S. Ji, J. Yang, Q. Yang, S. Liu, M. Chen and J. Zhao, J. Org. Chem.,
2009, 74, 4855–4865.
73 C. Yang, X. Zhang, H. You, L. Zhu, L. Chen, L. Zhu, Y. Tao, D. Ma,
Z. Shuai and J. Qin, Adv. Funct. Mater., 2007, 17, 651.
74 O. Wolfbeis and R. Narayanaswamy, Optical sensors: Industrial,
Environmental and Diagnostic Applications, Springer-Verlag, Berlin-
Heidelberg, 2004.
8 G. Coll, J. Morey, A. Costa and J. M. Sa a´ , J. Org. Chem., 1988, 53,
5
345.
9 M. J. Frisch, G. W. Trucks, H. B. Schlegel, et al. Gaussian 09 Revision
A.1, Gaussian Inc., Wallingford CT, 2009.
0 E. L. Williams, J. Li and G. E. Jabbou, Appl. Phys. Lett., 2006, 89,
0
83506.
1 J. R. Lakowicz, Principles of Fluorescence Spectroscopy, 2nd ed., Kluwer
Academic/Plenum Publishers, New York, 1999.
2 B. Valeur. Molecular Fluorescence: Principles and Applications,Wiley-
VCH, Verlag GmbH: New York, 2001.
75 H. Guo, S. Ji, W. Wu, W. Wu, J. Shao and J. Zhao, Analyst, 2010, 135,
2832.
76 E. R. Carraway, J. N. Demas, B. A. DeGraff and J. R. Bacon, Anal.
Chem., 1991, 63, 337–342.
77 L. A. Sacksteder, J. N. Demas and B. A. DeGraff, Anal. Chem., 1993,
65, 3480–3483.
78 D. V. Kozlov and F. N. Castellano, Chem. Commun., 2004, 2860.
79 R. R. Islangulov, D. V. Kozlov and F. N. Castellano, Chem. Commun.,
2005, 3776.
63 D. S. Tyson and F. N. Castellano, Inorg. Chem., 1999, 38, 4382.
64 S. M. Borisov and I. Klimant, Anal. Chem., 2007, 79, 7501.
6
5 S. Z a´ li sˇ , N. B. Amor and C. Daniel, Inorg. Chem., 2004, 43, 7978.
66 A. Gabrielsson, M. Busby, P. Matousek, M. Towrie, E. Hevia, L.
Cuesta, J. Perez, S. Z a´ li sˇ and A. Vl cˇ ek, Jr., Inorg. Chem., 2006, 45,
9
789.
6
7 J. Maurer, M. Linseis, B. Sarkar, B. Schwederski, M. Niemeyer, W.
Kaim, S. Z a´ li sˇ , C. Anson, M. Zabel and R. F. Winter, J. Am. Chem.
Soc., 2008, 130, 259.
80 (a) P. Du and Richard Eisenberg, Chem. Sci., 2010, 1, 502; (b) S. Ji,
W. Wu, W. Wu, H. Guo and J. Zhao, Angew. Chem., Int. Ed., 2011, 50,
1626.
6
6
8 Y. Liu, J. Feng and A. Ren, J. Phys. Chem. A, 2008, 112, 3157.
9 F. Han, L. Chi, X. Liang, S. Ji, S. Liu, F. Zhou, Y. Wu, K. Han, J. Zhao
and T. D. James, J. Org. Chem., 2009, 74, 1333.
0 X. Zhang, Y. Wu, S. Ji, H. Guo, P. Song, K. Han, W. Wu, W. Wu, T. D.
James and J. Zhao, J. Org. Chem., 2010, 75, 2578.
81 S. Baluschev, V. Yakutkin, T. Miteva, Y. Avlasevich, S. Chernov, S.
Aleshchenkov, G. Nelles, A. Cheprakov, A. Yasuda, K. M u¨ llen and G.
Wegner, Angew. Chem., Int. Ed., 2007, 46, 7693.
82 H. Chen, C. Hung, K. Wang, H. Chen, W. S. Fann, F. Chien, P. Chen,
T. J. Chow, C. Hsu and S. Sun, Chem. Commun., 2009, 4064.
7
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