Photostable Fluorophenyl-Substituted Cyclometalated Platinum(II) Emitters for Monitoring of Molecular Oxygen in Real Time

Article abstract of DOI:10.1021/acs.inorgchem.5b00775

The effects of fluorophenyl substituents on the photoluminescence, redox properties, and oxygen sensing behaviors of the cyclometalated Pt(II) complexes are reported. The Pt(II) complexes with fluorophenyl substituents at the para position on the phenyl r

Full text of DOI:10.1021/acs.inorgchem.5b00775

Article
pubs.acs.org/IC
Photostable Fluorophenyl-Substituted Cyclometalated Platinum(II)
Emitters for Monitoring of Molecular Oxygen in Real Time
Yang Xing, Chun Liu,* Jing-Hai Xiu, and Jiu-Yan Li
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Linggong Road 2, Dalian 116024, China
*
S Supporting Information
ABSTRACT: The effects of fluorophenyl substituents on the
photoluminescence, redox properties, and oxygen sensing
behaviors of the cyclometalated Pt(II) complexes are reported.
The Pt(II) complexes with fluorophenyl substituents at the
para position on the phenyl ring of 2-phenylpyridine (ppy)
exhibit higher oxygen sensitivities than those at the meta
position. Photodegradation tests demonstrate that the
introduction of fluorophenyl substituents can strongly improve
the photostability of cyclometalated Pt(II) complexes. Fast
response and recovery times of oxygen sensing films are
obtained in 3.0 s on going from 0% O to 100% O and in 4.0 s
2
2
on going from 100% O to 0% O (95% recovery of the
2
2
luminescence), respectively. The oxygen sensing films show excellent operational stability in 4000 s saturation O /N cycles,
2
2
which meets the requirement of monitoring molecular oxygen in real time.
INTRODUCTION
of OSPs. They also affect the π-conjugate of the intraligand and
■
provide steric protection around the metal, which is a main
Determination of molecular oxygen is of great importance in
various fields of science and technology.
3
4,35
20
1
−3
consideration for increasing the quantum yield.
Amao, and Borisov
Okura,
Compared with
19
13,14,16
have demonstrated that porphyrin
traditional analytical techniques, optical oxygen sensing can
provide advantages of simple, quick, and nondestructive
characteristics, low cost, small size, as well as low requirements
for instrumental implementation. Optical oxygen sensing is
based on the dynamic quenching process of the oxygen-
sensitive probes (OSPs) by molecular oxygen, which is fully
reversible and allows the determination of oxygen in real
ligands of Pt(II) complexes modified with fluorinated
substituents could enhance the photostability. As far as we
know, no efforts have been made to heighten the photostability
of OSPs by modification of the cyclometalated Pt(II)
complexes with a fluorinated substituent. Very recently, we
have successfully introduced a trifluoromethyl substituent (
4
−6
CF ) onto the cyclometalated Pt(II) complexes. And we found
3
time.
complexes are widely used due to their high photoluminescence
Among a variety of luminescent OSPs, Pt(II)
that the introduction of CF can effectively improve the
3
7
,8
photostability of the corresponding cyclometalated Pt(II)
quantum yields and significantly longer lifetimes. Pt(II)
36
complexes and reduce photo-oxidation.
porphyrin complexes have often been reported as OSPs in the
9
−20
In this paper, we introduce bulky fluorophenyl substituents
onto the cyclometalating ligand 2-phenylpyridine (ppy), such
as a 3,4,5-trifluorophenyl substituent, to improve the photo-
stability of corresponding cyclometalated Pt(II) complexes and
to enhance the photoluminescence (PL) by preventing self-
quenching and reducing photo-oxidation. In addition to that,
we are interested in examining how the position of a
fluorophenyl substituent affects the oxygen sensitivity of the
Pt(II) complex from the viewpoint of optical oxygen sensing.
Chemical structures of two series of the fluorophenyl-
substituted cyclometalated Pt(II) complexes LXP1−LXP3 and
LXM1−LXM3 are shown in Chart 1. These complexes possess
literature.
Only a few examples of cyclometalated Pt(II)
21−25
complexes were tested in oxygen sensing.
To allow smooth oxygen diffusion and minimize probe self-
quenching, OSPs are usually doped into an oxygen permeable
2
6
matrix. Typical matrices include ethyl cellulose, poly-
27
28,29
(
dimethylsiloxane), and polystyrene.
However, OSPs
immobilized in supporting matrices usually show a decrease
of luminescence intensity (poor photostability) under con-
tinuous illumination. The reason comes from the photo-
oxidation nature of OSPs. Efforts have been made to heighten
19
the photostability of OSPs by modifying matrices and
1
3−16,19,20
OSPs.
Notably, fluorinated matrices display large
2
-phenylpyridine with a fluorophenyl substituent at either the
permeability of oxygen and stability against irradiation which is
induced by the high electronegativity of fluorine. For example,
Amao et al. reported that fluorinated polymers were excellent
para or meta position of the phenyl ring.
19,30−33
matrices for oxygen sensing.
Fluorinated substituents
Received: April 7, 2015
can raise the oxidation potential and lower the electric density
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b00775
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Article
Chart 1. Structures of the Fluorophenyl-Substituted Pt(II) Complexes
Figure 1. Perspective views of LXP1, LXM1, LXM2, and LXM3 (30% probability ellipsoids, hydrogen atoms are omitted for clarity).
RESULTS AND DISSCUSSION
in Table 1 and Table S1 (see Supporting Information, SI). The
PtN distances are in the range 1.984(5)−1.996(5) Å, which
■
X-ray Structural Analysis. Single crystals suitable for X-ray
37,38
are slightly longer than those of common PtN bonds.
diffraction analysis have been grown by slow diffusion of hexane
into a chloroform solution of the complexes. Perspective views
of LXP1, LXM1, LXM2, and LXM3 are shown in Figure 1. Key
bonding parameters and selected crystallographic data are given
The PtC distance is 1.944(7)−1.976(6) Å. The CPtN
and OPtO angles are respectively 81.4(2)−81.9(2)° and
91.7(2)−92.1(2)°, which are similar to reported values (bond
B
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Table 1. Selected Bond Length (Å) and Angles (deg) around the Metal Core in the Pt(II) Complexes
a
complexes
LXP1
CCDC number
1038809
PtN
PtC
PtO
CPtN
OPtO
PtPt
1.984(5)
1.976(6)
2.073(5)
81.4(2)
91.7(2)
6.405(4)
4.469(5)
4.473(6)
4.466(5)
1
.994(4)
2.100(5)
.997(5)
2.103(3)
.992(3)
2.109(5)
.999(5)
LXM1
LXM2
LXM3
1000779
997714
1.996(5)
1.988(4)
1.994(6)
1.964(6)
1.962(5)
1.944(7)
81.5(2)
81.9(2)
81.9(2)
91.8(2)
91.7(2)
92.1(2)
1
1
1038810
1
a
The bond lengths in bold style are the PtO distances, where the O atoms of the acetylacetonate are trans to the C atoms of the fluorophenyl-
substituted 2-phenylpyridine.
Figure 2. [A] Absorption spectra and [B] Emission (PL) spectra of all the Pt(II) complexes. 10−5 mol L−1 in degassed CH Cl , 25 °C.
2
2
Table 2. Photophysical and Electrochemical Data of All Pt(II) Complexes
a
b
c
d
e
complexes
absorption λabs (nm)
emission λem (nm)
Φp
τr (μs)
ΔT (°C)
LXP1
237 (2.13), 255 (2.41), 296 (2.54), 334 (1.47), 366 (0.74), 405 (0.52)
238 (1.85), 257 (2.26), 295 (2.46), 334 (1.28), 367 (0.53), 405 (0.33)
235 (2.04), 257 (2.43), 291 (2.54), 333 (1.29), 374 (0.56), 405 (0.38)
229 (3.63), 278 (4.12), 365 (0.56), 397 (0.40)
525, 559
526, 563
526, 565
499, 531
496, 528
492, 526
0.18
0.15
0.22
0.14
0.22
0.20
0.15
4.11
2.45
1.39
2.23
1.74
1.03
276
258
271
272
278
282
LXP2
LXP3
LXM1
LXM2
229 (3.99), 279 (4.25), 361 (0.62), 397 (0.45)
LXM3
229 (4.12), 280 (4.12), 366 (0.60), 404 (0.41)
f
f
g
Pt(ppy)(acac)
229 (3.69), 250 (2.24), 277 (2.12), 314 (1.05), 365 (0.63), 389 (0.43)
486, 518
2.60
294
a
−5
4
−1
−1
b
Measured in CH Cl at a concentration of 10 M and extinction coefficients (10 M cm ) are shown in parentheses. The emission maxima
2
2
max
c
d
(λ
) are the values in bold style. In degassed CH Cl relative to [Ir(ppy) acac] (Φ = 0.34), (λ = 400 nm). Measured in degassed CH Cl at a
em
2
2
2
p
ex
2
2
−5
e
sample concentration of ca. 10 M and the excitation wavelength was set at 425 nm for all the samples at 25 °C. ΔT is the weight-reduction
temperature. Ref 39. Ref 38.
f
g
lengths and angles around the metal core in 7-F, 7-H, 7-Me, 7-
OMe, 9, and 11 in ref 38). The bond distances of the PtO
edge trans to C atom 2.073(5)−2.109(5) Å are longer
compared to those of the other PtO bonds 1.992(3)−
high energy, putting them under the more intense ligand-
centered (LC) transitions. Bands around 238 nm have similar
intensity (about 20 000 M− cm ) for LXP1−LXP3, while
1
−1
Pt(ppy)(acac) is stronger (37000 M− cm ). It is therefore
attributed to a π−π* transition involving the intraligand. UV−
visible absorption spectra of LXM1−LXM3 exhibit three major
absorption bands (Figure 2A and Table 2). The absorption
1
−1
1
.999(5) Å, due to the strong trans influence from the C atom
trans to O atom. The PtPt distances are beyond the range of
.7−3.5 Å. Thus, PtPt interaction is impossible in the crystal.
All other bond lengths around the Pt core are typical for
2
−
1
bands at 238 nm and at 250−300 nm (33 000−43 000 M
39
−1
cyclometalates and β-diketonate derivatives of Pt(II).
cm ) are due to the spin-allowed singlet transitions of the
intraligands. The singlet and triplet metal-to-ligand charge
UV−Visible Absorption Spectra and Emission Spectra.
UV−visible absorption spectra of LXP1−LXP3 have similar
band positions (Figure 2A and Table 2). They display strong
bands up to 300 nm belong to intraligand (π−π*) transitions.
Lower energy absorption bands at 360 nm attributed to singlet
1
3
transfer ( MLCT and MLCT) absorption bands appear at
>370 nm (ε < 10 000 M− cm ), with a peak position
1
−1
depended strongly on the identity of intraligand.
Fluorophenyl substituents at 2-phenylpyridine have signifi-
cant influences on the emission properties of the complexes.
We found that the emission maxima shifts to a longer
wavelength when introducing fluorophenyl substituents at
1
and triplet metal-to-ligand charge transfer ( MLCT and
3
MLCT) transitions with spin-forbidden. The strong ligand
field of the cyclometalating ligand shifts the d−d transitions to
C
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either the para (p-) (LXP1−LXP3) or meta (m-) (LXM1−
LXM3) position (Figure 2B and Table 2). The emission
maxima for LXP1−LXP3, LXM1−LXM3, and Pt(ppy)(acac)
are in region from 486 to 526 nm. The emission maxima are
red-shifted about 40 nm for LXP1 (525 nm), LXP2 (526 nm),
and LXP3 (526 nm) compared to the model emitter
Pt(ppy)(acac) (486 nm). The emission maxima are red-shifted
for LXM1 (499 nm), LXM2 (496 nm), and LXM3 (492 nm).
The photoluminescence quantum yields Φ of all complexes
p
range from 0.14 to 0.22 (Table 2).
Phosphorescence Lifetimes. The fluorophenyl substitu-
ents also have significant influence on phosphorescence
lifetimes (Table 2). The lifetimes of Pt(II) complexes range
from 1.03 to 4.11 μs. These lifetimes in the microsecond
regime suggest that triplet excited states contribute to light
emission; that is, the complexes emit phosphorescence. The
lifetimes decrease in the following order: LXP1 > LXM1; LXP2
>
LXM2; LXP3 > LXM3. The phosphorescence lifetime of
LXP1 (4.11 μs) become longer compared to Pt(ppy)(acac)
3
9
(
2.60 μs) when the 4-fluorophenyl group is at the para
position on the phenyl ring of 2-phenylpyridine. This result is
useful information for designing novel Pt(II) complexes with a
long lifetime. With the increase of fluorine atom on the
fluorophenyl substituent, however, phosphorescence lifetimes
are diminishing.
Electrochemical and Electronic Characterization.
LXP1−LXP3 and LXM1−LXM3 show irreversible oxidation
waves in the region of 0.65−0.71 V (Table 3 and SI Figure S1).
Table 3. Frontier Orbital Energy Levels of All Pt(II)
Complexes
a
b
c
d
complexes
Eox (V)
HOMO (eV)
LUMO (eV)
Eg (eV)
LXP1
0.65
0.66
0.70
0.66
0.67
0.71
0.53
−5.05
−5.06
−5.10
−5.06
−5.07
−5.11
−4.93
−2.57
−2.58
−2.64
−2.49
−2.48
−2.51
2.48
2.48
2.46
2.57
2.59
2.60
2.68
LXP2
Figure 3. Kohn−Sham HOMO and LUMO for LXP1−LXP3 and
LXM1−LXM3 for the ground state geometry at the DFT/M06/PCM
LXP3
LXM1
=
CH Cl level of theory.
2 2
LXM2
LXM3
Pt(ppy)(acac)
−2.25
−1
calculated energy levels in Figure 3 and Table 3 should not be
a
0.1 M [Bu N]PF in CH Cl , scan rate 100 mV s , measured using
4
6
2
2
overinterpreted, because the appropriate difference between
b
saturated calomel electrode (SCE) as the standard. EHOMO (eV) =
e(4.4 + E ). E
edge (λ ) of solid films by equation of E = 1240/λedge
40
experimental values and calculated values is acceptable.
c
d
−
= EHOMO + E . Estimated from the absorption
LUMO g
ox
Fitting Formula of Oxygen Sensing. Optical oxygen
sensors depend on the diffusion-controlled quenching of OSPs
by oxygen. Diffusion-controlled quenching is reflected by
Stern−Volmer eq 1. K is the quenching rate constant, and pO
.
edge
g
Compared to the oxidation potential (E ) of Pt(ppy)(acac)
ox
q
2
(
0.53 V), E for LXP1−LXP3 at 0.65 V, 0.66 V, 0.70 V, and for
ox
is the partial pressure of oxygen. I is the phosphorescence
intensity, and τ is the lifetime of an OSP. I and τ are the
LXM1-LXM3 at 0.66 V, 0.67 V, 0.71 V, show that the
0
0
introduction of a fluorophenyl substituent leads to effective
corresponding values in the absence of oxygen.
raise of E . The same result has been observed when
ox
I0
I
τ0
τ
introducing a trifluoromethyl substituent (CF ) on cyclo-
3
=
= 1 + K τ ·p
O2
q 0
36
(1)
metalated Pt(II) complexes.
4
1
Density Functional Theory (DFT) Calculations. The
DFT calculations in Figure 3 show that the HOMOs of LXP1−
LXP3 mainly consist of the platinum center, the phenyl ring of
For heterogeneous oxygen sensing, a two-site model eq 2
was required to fit the Stern−Volmer plots. There exist two
portions which are defined as f and f (f + f = 1). K and
1
2
1
2
SV1
2-phenylpyridine and acetyl acetone moiety, while the LUMOs
KSV2 are the quenching rate constants for two portions.
are on the rings of cyclometalating ligands. The HOMOs of
LXM1−LXM3 mainly consist of the platinum center, biphenyl
group of cyclometalating ligands and acetyl acetone moiety.
The LUMOs are on the 2-phenylpyridine and the platinum
center. The increase of strong electron-withdrawing group
f
f2
I
I0
τ
1
=
=
+
τ0
1 + KSV1·pO
1 + KSV2·pO
(2)
2
2
Parameter weighted quenching constant K aS pV p (K = f ×
KSV1 + f × KSV2) is the guide of the sensitivity of an oxygen
app
SV
1
(
−F) lower the energy level of LUMO and HOMO obviously
2
∧
by increasing the electron affinity of the C N ligand. These
sensor.
D
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Photostability of Oxygen Sensing Films. The photo-
stability of OSPs is of great importance for the detection of
oxygen concentrations under continuous irradiation. Hartmann
and co-workers reported the experimental method for photo-
degradation. In this work, the weight content of all Pt(II)
complexes immobilized in an ethyl cellulose (EC) film is 0.5 wt
Table 4. Oxidation Potentials for All the Pt(II) Complexes
a
b
c
complexes
LXP1
E00 (V)
Eox (V)
Eo*x (V)
2.36
2.35
2.35
2.49
2.50
2.52
2.55
0.65
0.66
0.70
0.66
0.67
0.71
0.53
−1.71
−1.69
−1.65
−1.83
−1.83
−1.81
−2.02
4
2
LXP2
LXP3
LXM1
LXM2
LXM3
%
. And the film thickness is about 5.88 μm. Photostability of
oxygen sensing films immobilized with Pt(II) complexes were
estimated upon continuous irradiation with a 254 nm 16 W UV
Pt(ppy)(acac)
lamp under air atmosphere. The power density on the films is
2
a
max
b
, scan rate 100 mV s−1,
2
3.4 W/m . After irradiation, the PL measurements performed
E00 = 1240/λem 0.1 M [Bu N]PF in CH Cl
4 6 2 2
measured using saturated calomel electrode (SCE) as the standard.
under N atmosphere. Data presented in Figure 4 indicate that
2
c
Eo*x = Eox − E00.
less reactive to photo-oxidation processes and increases its
photostability.
Time-Dependent Response of Oxygen Sensing Films.
The dynamic responses of oxygen sensing films were
investigated against small steps of O concentration variation
2
(
Figure 5). The oxygen sensing films in N exhibit intense
2
emission. All the films are sensitive to oxygen with the
phosphorescence intensity changing stepwise and reversibly to
different O concentrations. The oxygen sensing data were
2
fitted by the two-site model (Figure 6) and weighted quenching
app
constant KSV are summarized in SI Table S2. All of the large
quenchable components (f ) > 91% show the wide liner range.
1
app
−1
The oxygen sensing film of LXP1 (KSV = 0.0203 Torr )
provides outstanding oxygen sensitivity. The fluorophenyl
substituent at either the para or meta position on the phenyl
ring of 2-phenylpyridine could reduce the intermolecular
interaction of the complexes and prevent self-quenching
compared to Pt(ppy)(acac), resulting in increased oxygen
sensitivities. Overall, the oxygen sensitivities are in the
following order: LXP1 > LXM1; LXP2 > LXM2; LXP3 >
LXM3. The fluorophenyl group at para position on the phenyl
ring of 2-phenylpyridine (LXP1−LXP3) demonstrated higher
oxygen sensitivities than meta position (LXM1−LXM3). The
oxygen sensitivities are consistent with their triplet lifetimes.
Operational Stability of Oxygen Sensing Films. Figure
7 shows an operational stability test conducted by luminescence
Figure 4. Photodegradation histograms of oxygen sensing films
immobilized with Pt(II) complexes. The power density on the films is
2
2
3.4 W/m .
photostability of fluorophenyl substituted Pt(II) complexes
LXP1−LXP3 and LXM1−LXM3) is much higher than that of
(
Pt(ppy)(acac) after 60 min irradiation. In fact, decreases in
intensity of LXP1−LXP3 by 24.9%, 24.8%, and 19.4% are
observed compared to Pt(ppy)(acac) by 41%. While decreases
in intensity of LXM1−LXM3 by 28.4%, 27.6%, and 21.2% are
observed after 60 min irradiation. With the increase of the
fluorine atom at the fluorophenyl substituent, Pt(II) complexes
demonstrate higher photostability.
In general, the photo-oxidation reactivity of the Pt(II)
complexes is determined by its excited-state oxidation
intensity of oxygen sensing film of LXP3. The I and I100 of an
0
4
3
potential. The zero−zero emission energy (E ), the
oxygen sensing film is constant, and the quenching and
recovering cycles are fully reversible, which exhibits excellent
0
0
ground-state oxidation potential (E ), and the excited-state
ox
oxidation potential (E*) of a Pt(II) complex can be estimated
operational stability in 12 cycles when N and O are switched
2 2
ox
4
4
from eq 3:
in 4000 s. Very fast response time of LXP3 immobilized in EC
was obtained at 3.0 s on going from 0% O to 100% O and
2
2
*
recovery time at 4.0 s (95% recovery of the luminescence) on
E
= Eox − E00
(3)
ox
going from 100% O2 to 0% O , which can meet the
2
Using the emission maxima (λ me ma x) of the Pt(II) complexes as
calculation of E00 together with the E in Table 3, the E* was
calculated (Table 4). It is clear that the E* of Pt(II) complexes
are in the sequence of LXP3 > LXP2 > LXP1 > Pt(ppy)(acac);
LXM3 > LXM2 = LXM1 > Pt(ppy)(acac). Notably, for the
Pt(II) complexes with same number of fluorine atom, para-
fluorophenyl substituents on the phenyl ring cause a greater
requirement of monitoring molecular oxygen in real time.
ox
ox
CONCLUSIONS
ox
■
In summary, six new fluorophenyl-substituted Pt(II) complexes
(LXP1−LXP3 and LXM1−LXM3) have been synthesized and
characterized by means of spectroscopic and electrochemical
methods and X-ray crystal structure. All Pt(II) complexes
exhibit intense phosphorescence emissions at room temper-
ature. By changing the position of fluorophenyl substituents,
the emission maxima were tuned in the wavelength region from
492 to 526 nm. The oxygen sensitivity of Pt(II) complexes was
evaluated according to the Stern−Volmer equation. The
fluorophenyl substituents at the para position on the phenyl
ring of ppy provided higher oxygen sensitivities than those at
the meta position. Fast response time at 3.0 s on going from 0%
anodic shift of E* than meta-fluorophenyl substituents (LXP1 >
ox
LXM1; LXP2 > LXM2; LXP3 > LXM3). The order is
consistent with the photostability order of the Pt(II) complexes
in photodegradation test (Figure 4). Although there are errors
in the E00 values caused by the calculation method, the errors
did not affect the order of E*. Hence the inductive effect of the
fluorophenyl substituents raises the excited-state oxidation
potentials of the Pt(II) complexes, which makes the molecules
ox
E
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Figure 5. Time-dependent emission intensity response of oxygen sensing films of all the Pt(II) complexes immobilized in EC under stepwise change
O concentrations, 25 °C, slit width = 2.5/2.5 nm.
2
ex/em
Figure 6. Stern−Volmer plots for the oxygen sensing films of all the
Pt(II) complexes immobilized in EC. Intensity ratios I /I versus O
Figure 7. Time trace curve of LXP3 immobilized in EC to O
saturation cycles, 25 °C, slit widthex/em = 2.5/2.5 nm.
/N
2 2
0
2
partial pressure.
O to 100% O and recovery time at 4.0 s on going from 100%
chemicals were purchased from commercial sources and used without
2
2
1
13
O to 0% O (95% recovery of the luminescence) were
further purification. H NMR and C NMR spectra were recorded on
a 400 MHz Varian Unity Inova spectrophotometer. Mass spectra were
recorded with a MALDI micro MX spectrometer. Phosphorescence
lifetimes were determined on a steady and transient state fluorometer
2
2
observed. Importantly, the introduction of a fluorophenyl
substituent can strongly improve the photostability of cyclo-
metalated Pt(II) complexes to reduce photo-oxidation. These
results are important information for designing novel photo-
stable OSPs for monitoring of molecular oxygen in real time.
(
FLS920, Edinburgh Analytical Instruments Ltd.). Thermogravimetric
analysis (TGA) was performed on a TGA Q500 instruments. The
Pt(II) complexes were stored at 30 °C for 10 min, then heated at a
heating rate of 10 °C/min under nitrogen atmosphere. Absorption
spectra were recorded by Lambda 750S UV/vis/NIR spctrometer
(PerkinElmer). Emission spectra were recorded by HITACHI F-7000
fluorescence spectrophotometer. Cyclic voltammograms of all the
Pt(II) complexes were recorded on an electrochemical workstation
(BAS100B/W, USA) at room temperature.
EXPERIMENTAL SECTION
■
Materials and Methods. Unless otherwise noted, all of the cross-
coupling reactions for preparing the ligands were carried out in air. 2-
Bromopyridine was purchased from Alfa Aesar. Fluorohenyl boronic
acids were purchased from Trusyn Chem-Tech Co., Ltd., China. Other
F
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Synthetic procedure of cyclometalated Pt(II) complexes LXP1−
LXP3 and LXM1−LXM3: The cyclometalating ligand (0.20 mmol)
was reacted with 1.2 equiv K PtCl (0.24 mmol, 99.0 mg) in a mixture
of 2-ethoxyethanol and water (6 mL/2 mL) at 100 °C for 16−24 h to
afford a platinum dimer, which was subsequently reacted with 10 equiv
Oxygen Sensing. General procedure of oxygen sensing film on
0.5% weight percents: EC (9.95 mg) was dissolved in CH Cl (0.90
2
2
mL) and then 0.10 mL LXP1 (0.5 mg/mL) in CH Cl was added to
2
4
2
2
the solution. After thoroughly mixing, the solution (0.10 mL) was
coated on a transparent quartz plate (r = 7.0 mm) and slowly
evaporated at room temperature. The film was dried for 24 h to
remove the potential cocrystallized solvent molecules before oxygen
sensing experiments. Then a yellow transparent EC oxygen sensing
film was obtained. The thickness of the film is about 5.88 μm.
The specific concentrations of oxygen in nitrogen at atmospheric
pressure (from 0−100% in volume fraction) were generated with two
tube flowmeter (Figure 8A). The transparent quartz plate (Figure 8B)
of the chelating diketone (1 mmol, 102.5 μL) and 10 equiv of Na CO3
2
(
1 mmol, 0.106 g) in 2-ethoxyethanol at 100 °C for 18−24 h.
1
LXP1: yellow solid; yield 70.0%. H NMR (400 MHz, CDCl ): δ
3
9
.01 (d, J = 5.5 Hz, 1H), 7.86−7.74 (m, 2H), 7.70−7.60 (m, 3H), 7.49
(
d, J = 8.1 Hz, 1H), 7.28 (s, 1H), 7.13 (t, J = 8.5 Hz, 3H), 5.49 (s,
1
1
1
H), 2.02 (s, 6H). 13C NMR (101 MHz, CDCl ): δ 185.8, 184.2,
3
67.9, 163.7, 161.2, 147.3, 143.8, 140.8, 139.2, 138.2, 128.9, 123.3,
22.6, 121.1, 118.4, 115.5, 115.3, 102.5, 28.2, 27.2. HRMS (ESI):
+
C H FNO Pt. Calcd.: 543.1044 [M + H] . Found: 543.1043 [M +
H] .
2
2
19
2
+
1
LXP2: yellow solid; yield 65.0%. H NMR (400 MHz, CDCl ): δ
3
9.02 (dd, J = 5.8, 0.8 Hz, 1H), 7.82 (td, J = 8.0, 1.5 Hz, 1H), 7.76 (d, J
=
7
(
1.8 Hz, 1H), 7.64 (d, J = 7.8 Hz, 1H), 7.53−7.44 (m, 2H), 7.44−
.35 (m, 1H), 7.22 (m, 2H), 7.13 (ddd, J = 7.3, 5.9, 1.4 Hz, 1H), 5.49
s, 1H), 2.03 (d, J = 3.6 Hz, 6H). 13C NMR (101 MHz, CDCl ): δ
3
1
1
2
85.9, 184.3, 167.7, 147.4, 144.4, 139.6, 139.4, 138.9, 138.9, 138.2,
28.7, 123.3, 122.5, 121.3, 118.5, 117.3, 117.2, 116.2, 116.0, 102.6,
+
8.2, 27.2. HRMS (ESI): C H F NO Pt. Calcd.: 561.0953 [M + H] .
2
2
18
2
2
+
Found: 561.0949 [M + H] .
1
LXP3: yellow solid; yield 73.1%. H NMR (400 MHz, CDCl ): δ
3
9.03 (d, J = 5.1 Hz, 1H), 7.83 (td, J = 8.0, 1.5 Hz, 1H), 7.73 (d, J = 1.9
Hz, 1H), 7.64 (d, J = 8.0 Hz, 1H), 7.49 (d, J = 8.0 Hz, 1H), 7.29 (dd, J
9.0, 6.6 Hz, 2H), 7.22 (dd, J = 8.0, 1.9 Hz, 1H), 7.15 (ddd, J = 7.3,
=
13
5.9, 1.4 Hz, 1H), 5.50 (s, 1H), 2.03 (d, J = 5.9 Hz, 6H). C NMR
(
101 MHz, CDCl ): δ 185.9, 184.3, 167.5, 150.1, 147.5, 145.0, 139.6,
3
1
1
+
38.6, 138.3, 137.9, 128.5, 123.4, 122.3, 121.5, 118.6, 111.2, 111.0,
02.6, 28.2, 27.2. HRMS (ESI): C H F NO Pt. Calcd.: 579.0856 [M
2
2
17
3
2
Figure 8. (A) N and O tube flowmeters. (B) The transparent quartz
2
2
+
+
H] . Found: 579.0963 [M + H] .
LXM1: yellow solid; yield 73.2%. H NMR (400 MHz, CDCl ): δ
plate whose inner surface is covered with oxygen sensing film. (C) The
home-assembled sealed flow cell in which transparent quartz plate is
placed.
1
3
9
.03 (dd, J = 5.8, 0.8 Hz, 1H), 7.83 (td, J = 8.0, 1.5 Hz, 1H), 7.73−7.67
(
m, 2H), 7.58 (td, J = 5.3, 2.7 Hz, 3H), 7.40 (dd, J = 7.9, 1.9 Hz, 1H),
13
7
.17−7.09 (m, 3H), 5.49 (s, 1H), 2.02 (d, J = 3.7 Hz, 6H). C NMR
(
101 MHz, CDCl ): δ 185.8, 184.2, 168.0, 163.3, 160.9, 147.4, 145.2,
coated with oxygen sensing film was placed into our home-assembled
sealed flow cell (Figure 8C). Dead volume of the flow cell is 0.1 mL.
The time trace curves and dynamic emissive intensity response of all
the Pt(II) oxygen sensing films were recorded by HITACHI F-7000
3
138.2, 137.9, 135.7, 131.1, 128.3, 121.5, 121.4, 118.4, 115.6, 115.4,
+
102.5, 28.3, 27.1. HRMS (EI): C H FNO Pt. Calcd.: 542.0969 [M] .
22
18
2
+
Found: 542.0966 [M] .
1
36
LXM2: yellow solid; yield 55.5%. H NMR (400 MHz, CDCl ): δ
fluorescence spectrophotometer.
3
9
2
2
.04 (d, J = 5.1 Hz, 1H), 7.89−7.81 (m, 1H), 7.70 (dd, J = 7.9, 3.2 Hz,
H), 7.56 (d, J = 1.8 Hz, 1H), 7.47−7.30 (m, 3H), 7.24−7.13 (m,
ASSOCIATED CONTENT
Supporting Information
13
■
H), 5.50 (s, 1H), 2.03 (d, J = 3.3 Hz, 6H). C NMR (101 MHz,
*
S
CDCl ): δ 185.9, 184.2, 167.8, 147.5, 145.3, 139.0, 138.3, 134.6, 131.2,
3
X-ray crystallographic data of LXP1, LXM1, LXM2, and LXM3
in CIF format. Detailed synthetic schemes and procedures;
characterization data; and crystal data for LXP1, LXM1, LXM2,
and LXM3. The Supporting Information is available free of
charge on the ACS Publications website at DOI: 10.1021/
acs.inorgchem.5b00775.
127.9, 122.5, 122.4, 121.6, 121.4, 118.5, 117.5, 117.3, 115.6, 115.4,
1
02.6, 28.3, 27.1. HRMS (EI): C H F NO Pt. Calcd.: 560.0875
22
17
2
2
+
+
[
M] . Found: 560.0884 [M] .
1
LXM3: yellow solid; yield 50.0%. H NMR (500 MHz, CDCl ): δ
3
9
7
7
2
1
1
.04 (d, J = 5.6 Hz, 1H), 7.85 (dd, J = 11.3, 4.2 Hz, 1H), 7.70 (d, J =
.9 Hz, 2H), 7.53 (d, J = 1.5 Hz, 1H), 7.34 (dd, J = 7.9, 1.7 Hz, 1H),
.22 (dd, J = 8.7, 6.6 Hz, 2H), 7.17 (t, J = 6.2 Hz, 1H), 5.50 (s, 1H),
.03 (d, J = 3.8 Hz, 6H). 13C NMR (101 MHz, CDCl ): δ 185.9,
3
AUTHOR INFORMATION
Corresponding Author
*E-mail: cliu@dlut.edu.cn.
■
84.3, 167.6, 152.7, 150.2, 147.5, 145.5, 140.0, 138.4, 133.6, 131.3,
27.6, 121.7, 121.1, 118.5, 110.5, 110.3, 102.6, 28.2, 27.1. HRMS (EI):
+
+
C H F NO Pt. Calcd.: 578.0781 [M] . Found: 578.0787 [M] .
22
16
3
2
Density Functional Theory (DFT) Calculations. The structures
Notes
of the complexes were optimized using density functional theory
The authors declare no competing financial interest.
(
set.
DFT) with the B3LYP functional and 6-31G(d)/LanL2DZ basis
2
3−25
Calculations have been carried out considering solvent effects
ACKNOWLEDGMENTS
The authors thank the financial support from the National
Natural Science Foundation of China (21276043, 21421005).
4
5,46
■
(
CH Cl ) with the polarizable continuum model (PCM).
The 6-
2
2
3
1G(d) basis set was employed for C, H, N, O, and the LanL2DZ
basis set was used for Pt(II). All these calculations were performed
with the Gaussian 09 software package.
47
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