Novel triphenylamine-based cyclometalated platinum(II) complexes for efficient luminescent oxygen sensing

Article abstract of DOI:10.1016/j.dyepig.2013.09.030

Novel triphenylamine-based cyclometalated Pt(II) complexes containing a pyridyl moiety have been synthesized and fully characterized. The cyclometalating ligands were prepared via an efficient palladium-catalyzed ligand-free Suzuki reaction of 4-(diphenyl

Full text of DOI:10.1016/j.dyepig.2013.09.030

Dyes and Pigments 101 (2014) 85e92
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Dyes and Pigments
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Novel triphenylamine-based cyclometalated platinum(II) complexes
for efficient luminescent oxygen sensing
*
Chun Liu , Xinlong Song, Xiaofeng Rao, Yang Xing, Zhonggang Wang, Jianzhang Zhao,
Jieshan Qiu
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Linggong Road 2, Dalian 116024, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel triphenylamine-based cyclometalated Pt(II) complexes containing a pyridyl moiety have been
synthesized and fully characterized. The cyclometalating ligands were prepared via an efficient
palladium-catalyzed ligand-free Suzuki reaction of 4-(diphenylamino)phenylboronic acid with 2-pyridyl
bromides under aerobic and aqueous conditions. The photophysical properties of the complexes
exhibited that introducing an electron-withdrawing group like trifluoromethyl or cyano group on the 5-
position of the pyridine ring affected the LUMO level of the Pt(II) complex significantly, resulting in a
marked decrease in energy gap. Moreover, the complex with a cyano group at the 5-position imparts a
substantial red-shift up to 56 nm. The O2 sensitivity of the complexes was quantitatively evaluated in a
Received 16 August 2013
Received in revised form
18 September 2013
Accepted 19 September 2013
Available online 4 October 2013
Keywords:
Phosphorescence
Luminescence
Oxygen sensor
Platinum
Triphenylamine
Ligand-free Suzuki reaction
polymer film. The results of the O2-sensing sensitivity of the Pt(II) complexes demonstrated that the
app
complex with a nitrile ligand exhibited the highest sensitivity (K
¼ 0.102 Torrꢀ1). The triphenylamine-
SV
based cyclometalated Pt(II) complexes are potential candidates for efficient luminescent oxygen sensing.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
attention since they may be potentially used as advanced functional
materials for organic light-emitting devices (OLEDs), dye-sensitized
Luminescence oxygen sensors have potential application in a
variety of fields, such as chemical industry, clinical analysis, envi-
ronmental monitoring, oceanography, and biology [1e9]. One of the
main composes of an oxygen sensor is the transition-metal complex,
which is usually immobilized on a polymer film [10e12] and acts as
an oxygen sensitizer because oxygen diffuses from the surrounding
medium into the film and plays a role as a powerful quencher of the
electronically excited state of the metal complex [11]. In 1985, a new
optical method based on phosphorescence lifetime quenching was
used for the measurement of oxygen in biological systems [13]. The
photophysical and photochemical properties of phosphorescent
transition-metal complexes with a long lifetime in the range of
microseconds including cyclometalated Ru(II), Ir(III), and Pt(II)
complexes are ideal for luminescence O2 sensing [5,14e16].
Ruthenium-tris(dipyridyl)dichloride is the first reported Ru(II)
complex foroxygen sensor with an indicatorembedded in silica [17].
In 1996, Marco and co-workers reported the first use of an Ir(III)
complex as the active species in the luminescence oxygen sensor
[18]. Luminescent Pt(II) complexes have also attracted much
solar cells, oxygen sensors, and photoreceptors in biological mole-
cules [19e28]. In 1991, the Pt(II) complexes were first applied for the
fiber-optic oxygen sensor [29]. Although avariety of Pt(II) complexes
with porphyrin ligands found application in optical sensors [10,30e
32], only few Pt(II) complexes from other cyclometalating ligands
were reported [33].
Triphenylamine (TPA) derivatives, due to the non-coplanarity of
the three phenyl substituents, strong electron-donating nature, good
hole-transporting capability and high light-to-electrical energy-
conversion efficiency, are important structural motifs in numerous
organic electroluminescence materials [34e39]. In 2009, Chan and
co-workers reported the first use of Ir(ppy-NPh2)3 complex for
luminescence oxygen sensing [40]. Later, Zhao et al. synthesized
Pt(ppy-NPh2)(acac) complex, which was the first example of a Pt(II)
complex containing a TPA moiety for oxygen sensing [16]. To the best
of ourknowledge, noreporton the structureefunction relationship of
Pt complex with a substituent at the pyridyl ring of the ppy-NPh2
cyclometalatingligand hasbeendescribedintheliterature. Therefore,
further investigation isnecessary to elucidate the meritsof TPA-based
cyclometalated Pt(II) complexes for oxygen sensing.
In the present paper, we describe the synthesis, structures and
photoelectric performances of novel cyclometalated platinum
* Corresponding author. Tel.: þ86 411 84986182.
E-mail address: chunliu70@yahoo.com (C. Liu).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.09.030

86
C. Liu et al. / Dyes and Pigments 101 (2014) 85e92
Scheme 1. Structures of the cyclometalated Pt(II) complexes featuring triphenylamine derivatives. i) K2PtCl4, 2-ethoxyethanol/water (3:1, v/v), N2, 100 ꢁC, 24 h; ii) Hacac, Na2CO3, 2-
ethoxyethanol, N2, 100 ꢁC, 24 h.
complexes with 4-(2-pyridyl)- substituted TPA derivatives (Scheme
1). The TPA derivatives used in this study were prepared efficiently
via a palladium-catalyzed ligand-free and aerobic Suzuki reaction
in aqueous ethanol developed by our group recently [41], which
will be used to investigate the relationship of structureephoto-
electric properties of the novel Pt(II) complexes and to evaluate the
performances in oxygen sensing.
phenylboronic acid (0.375 mmol, 0.108 g), 2 equiv of K2CO3
(0.5 mmol, 0.069 g), Pd(OAc)2 (1.5 mol%, 0.00375 mmol, 0.84 mg),
ethanol/water (3 mL/1 mL) was stirred at 80 ꢁC in air for indicated
time. The reaction mixture was added to brine (15 mL) and
extracted four times with ethyl acetate (4 ꢂ 15 mL). The solvent was
concentrated and the product was isolated by short-column chro-
matography. The cyclometalating ligand was reacted with 1.2 equiv
K2PtCl4 (0.2 mmol, 83.02 mg) in a mixture of 2-ethoxyethanol and
water (6 mL/2 mL) at 80 ꢁC for 16e24 h to afford a platinum dim-
mer, which was subsequently reacted with 5 equiv of the chelating
2. Experimental
diketone (0.1 mmol, 102.5 mL) and 10 equiv of Na2CO3 (1 mmol,
2.1. Materials and instruments
0.106 g) in 2-ethoxyethanol at 100 ꢁC for 18e24 h.
LSTP-1 [39]. Eluent: CH2Cl2/hexane (1:1, v/v). A yellow solid;
All the cross-coupling reactions for preparing the ligands were
carried out in air. 2-Bromopyridines were purchased from Alfa
Aesar. 4-(Diphenylamino) phenylboronic acid was purchased from
Trusyn Chem-Tech Co., Ltd., China. Other chemicals were purchased
from commercial sources and used without further purification. 1H
NMR and 13C NMR spectra were recorded on a 400 MHz Varian
Unity Inova spectrophotometer. Mass spectra were recorded with a
MALDI micro MX spectrometer. The intensities of the crystal data
yield: 70.2%. 1H NMR (400 MHz, CDCl3):
d
¼ 8.87 (d, J ¼ 5.2 Hz, 1H,
Py), 7.71 (t, J ¼ 7.7 Hz, 1H, Ph), 7.47 (d, J ¼ 7.8 Hz, 1H, Py), 7.24e7.29
(m, 5H, Py and Ph), 7.18e7.24 (m, 5H, Ph), 6.97e7.05 (m, 3H, Ph),
6.76 (d, J ¼ 8.4 Hz, 1H, Ph), 5.38 (s, 1H, CH), 1.96 (s, 3H, CH3), 1.72 (s,
3H, CH3).
LSTP-2. Eluent: CH2Cl2/hexane (3:1, v/v). A yellow solid; yield:
38.4%; 1H NMR (400 MHz, CDCl3):
d
¼ 8.67 (d, J ¼ 6.0 Hz, 1H, Py),
7.26e7.27 (m, 2H, Ph), 7.21e7.24 (m, 2H, Py), 7.00e7.20 (m, 5H, Ph),
6.80e7.00 (m, 4H, Ph), 6.76 (d, J ¼ 6.8 Hz, 1H, Ph), 6.74 (dd,
J ¼ 2.3 Hz, 1H, Ph), 5.37 (s, 1H, CH), 2.40 (s, 3H, CH3), 1.95 (s, 3H,
were collected on a Bruker SMART APEX II CCD diffractometer with
ꢀ
graphite-monochromated Mo-Ka (
l
¼ 0.71073 A) using the SMART
and SAINT programs. UV/Vis absorption spectra were recorded on
an HP8453 UV/Vis spectrophotometer. Fluorescence spectra were
recorded with a PTI-700 spectrofluorimeter. Luminescent quantum
yields were measured with [Ir(ppy)3] (UP ¼ 0.40, lex ¼ 400 nm, in
CH2Cl2, under degassed conditions). Phosphorescence lifetimes
were measured on an Edinburgh FLS920 Spectrometer in a
degassed dichloromethane solution with excitation wavelength at
410 nm. Cyclic voltammograms of the Pt(II) complexes were
recorded on an electrochemical workstation (BAS100B/W, USA) at
room temperature in a 0.1 M [Bu4N]PF6 solution under nitrogen gas
protection.
CH3), 1.70 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3):
d
¼ 185.50,
183.97 (CO), 167.18, 149.59, 148.16, 147.59, 146.41, 139.70, 138.23,
129.19, 129.06, 124.16, 123.64, 123.25, 120.99, 118.32, 117.62 (Ar),
102.24 (CH), 28.23, 26.82, 21.57 (CH3). HRMS (EI): calcd. for
C
29H26N2O2Pt [M]þ 629.1642; found: 629.1655.
LSTP-3. Eluent: CH2Cl2/hexane (3:1, v/v). A yellow solid; Yield:
27.8%. 1H NMR (400 MHz, CDCl3):
7.25e7.32 (m, 4H, Ph), 7.18e7.25 (m, 7H, Py and Ph), 7.02 (t,
d
¼ 7.53 (t, J ¼ 7.8 Hz, 1H, Py),
2.2. Synthesis of the cyclometalated Pt(II) complexes
Cyclometalating ligands with a TPA moiety L-1eL-7 were syn-
thesized according to an efficient ligand-free Suzuki reaction [41],
which were then used to synthesize new Pt(II) complexes via two
distinctive steps as previously reported (Scheme 1) [42]. Synthetic
procedure of cyclometalating ligands L-1eL-7: a mixture of 2-
pyridyl bromide (0.25 mmol), 1.5 equiv of 4-(diphenylamino)
Scheme 2. The structure of polymer IMPES-C for this study.

C. Liu et al. / Dyes and Pigments 101 (2014) 85e92
87
J ¼ 7.2 Hz, 2H, Ph), 6.81 (d, J ¼ 7.0 Hz, 1H, Ph), 6.75 (dd, J ¼ 8.4 Hz,
26.58, 24.87 (CH3). HRMS (EI): calcd. for C29H26N2O2Pt [M]þ
629.1642; found: 629.1620.
1H, Ph), 5.39 (s, 1H, CH), 2.91 (s, 3H, CH3), 1.88 (s, 3H, CH3), 1.62 (s,
3H, CH3). 13C NMR (100 MHz, CDCl3):
d
¼ 185.36, 183.51 (CO),
LSTP-4. Eluent: CH2Cl2/hexane (3:1, v/v). A yellow solid; Yield:
168.82, 163.19, 147.56, 147.41, 139.28, 137.42, 137.28, 129.08, 125.53,
123.77, 123.13, 122.04, 121.90, 117.56, 114.67 (Ar), 101.33 (CH), 28.01,
41.6%. 1H NMR (400 MHz, CDCl3):
d
¼ 8.68 (s, 1H, Py), 7.55 (d,
J ¼ 7.8 Hz, 1H, Ph), 7.37 (d, J ¼ 8.3 Hz, 1H, Py), 7.26e7.35 (m, 6H, Ph),
7.17e7.20 (m, 4H, Py and Ph), 7.01e7.03 (t, J ¼ 7.2 Hz, 2H, Ph), 6.75
(dd, J ¼ 8.4 Hz, 1H, Ph), 5.38 (s, 1H, CH), 2.36 (s, 3H, CH3), 1.97 (s, 3H,
CH3), 1.71 (s, 3H, CH3). 13C NMR (100 MHz, CDCl3):
d
¼ 185.60,
184.04 (CO), 165.15, 147.86, 147.64, 146.85, 139.07, 138.76, 138.49,
129.98, 129.07, 125.26, 123.42, 123.38, 122.97, 117.82, 117.28 (Ar),
102.29 (CH), 28.31, 26.83, 18.20 (CH3). HRMS (EI): calcd. for
C
29H26N2O2Pt [M]þ 629.1642; found: 629.1592.
LSTP-5. Eluent: CH2Cl2/hexane (3:1, v/v). A yellow solid; Yield:
40.6%. 1H NMR (400 MHz, CDCl3):
Ph), 7.44 (m, 1H, Ph), 7.26e7.28 (m, 2H, Py), 7.20e7.25 (m, 8H, Ph),
7.03e7.17 (t, J ¼ 7.2 Hz, 2H, Ph), 6.76 (d, J ¼ 8.4 Hz, 1H, Ph), 5.39 (s,
1H, CH), 1.97 (s, 3H, CH3), 1.72 (s, 3H, CH3). 13C NMR (100 MHz,
d
¼ 8.82 (s, 1H, Py), 7.54 (m, 1H,
CDCl3):
d
¼ 185.90, 184.13 (CO), 164.79, 157.53, 155.06, 148.36,
147.45, 138.96, 136.93, 135.70, 135.38, 129.12, 125.53, 125.46, 125.34,
123.84,123.23,123.03,118.12,118.06,117.55 (Ar),102.42 (CH), 28.23,
26.75 (CH3). HRMS (EI): calcd. for C28H23N2O2PtF [M ꢀ H]ꢀ
632.1313; found: 632.1341.
LSTP-6. Eluent: CH2Cl2/hexane (3:1, v/v). A yellow solid; Yield:
50.3%. 1H NMR (400 MHz, CDCl3):
d
¼ 9.14 (s, 1H, Py), 7.86 (dd,
J ¼ 8.6 Hz, 1H, Ph), 7.50 (d, J ¼ 8.6 Hz, 1H, Ph), 7.25e7.31 (m, 5H, Py
and Ph), 7.17e7.25 (m, 5H, Ph), 7.06e7.10 (m, 3H, Ph), 6.75 (dd,
J ¼ 8.5 Hz,1H, Ph), 5.40 (s,1H, CH),1.98 (s, 3H, CH3),1.71 (s, 3H, CH3).
13C NMR (100 MHz, CDCl3):
d
¼ 186.09, 184.10 (CO), 170.95, 149.82,
147.00, 144.39, 141.88, 135.37, 134.56, 129.24, 126.10 (Ar), 125.39
(CF3), 123.90, 121.65, 117.10, 116.49, 103.82 (Ar), 102.40 (CH), 28.24,
26.71 (CH3). HRMS (EI): calcd. for C29H23N2O2PtF3 [M]ꢀ 683.1359;
found: 683.1378.
LSTP-7. Eluent: CH2Cl2/hexane (2:1, v/v). A red solid; Yield:
36.7%. 1H NMR (400 MHz, CDCl3):
J ¼ 8.4 Hz, 1H, Ph), 7.32 (d, J ¼ 8.9 Hz, 1H, Py), 7.29 (s, 1H, Ph), 7.20e
7.25 (m, 7H, Py and Ph), 7.11e7.20 (m, 4H, Ph), 6.74 (d, J ¼ 14.8 Hz,
1H, Ph), 5.40 (s, 1H, CH), 2.00 (s, 3H, CH3), 1.71 (s, 3H, CH3). 13C NMR
d
¼ 9.13 (s, 1H, Py), 7.85 (d,
(100 MHz, CDCl3):
d
¼ 186.27, 184.16 (CO), 171.08, 150.52, 150.32,
146.66, 143.05, 139.81, 134.51, 129.31, 126.40, 124.32, 120.93, 117.09,
116.13, 116.09, 111.35 (Ar), 103.71 (CN), 102.51 (CH), 28.26, 26.67
(CH3). HRMS (EI): calcd. for C29H23N3O2Pt [M]þ 640.1438; found:
640.1451.
2.3. Luminescent oxygen sensing
A home-assembled flow cell and optical fiber were used for the
oxygen sensing. Typical oxygen film preparation is as follows.
IMPES-C polymer (Scheme 2) (10.0 mg) prepared according to the
literature [7] was dissolved in acetone (0.5 mL) and then the Pt
complex in CH2Cl2 (0.2 mL, 1.0 ꢂ 10ꢀ3 mol dmꢀ3) was added to the
solution. After thoroughly mixing, about 0.3 mL of the solution was
coated on a silica glass disk (diameter 1.6 cm). The solvent was
evaporated at room temperature and a transparent film was ob-
tained. The thickness of the film containing LSTP-1 was estimated
to be 15.8 mm from the weight of the film (6.1 mg) and the density
of the polymer (1.21 g cmꢀ3). The film thicknesses of the complexes
LSTP-2eLSTP-7 were estimated by the same method to be 16.0,17.3,
15.9, 16.3, 15.8, and 18.0 mm, respectively.
3. Results and discussion
3.1. Crystal structures
To further establish their molecular structures, a majority of
these Pt(II) complexes were subjected to X-ray single-crystal
Fig. 1. Perspective view of the crystal structure of Pt(II) complexes (30% probability
ellipsoids, hydrogen atom labels have been omitted for clarity).

88
C. Liu et al. / Dyes and Pigments 101 (2014) 85e92
Table 1
heavy metal center, which are not observed in the free ligands. It is
likely that the strong ligand field of the cyclometalating ligands
shifts the ded transitions to high energy, putting them under the
more intense ligand-centered (LC) transitions. The substituents on
the N,N-diphenyl-4-(pyridin-2-yl)aniline have significant influence
on the absorption properties of the complexes. The lower-lying
band is shifted upon the attachment of different substituents on
the pyridyl ring in the order: LSTP-7 (lmax ¼ 474 nm) > LSTP-6
(451 nm) > LSTP-5 (427 nm) > (LSTP-1 (424 nm), LSTP-3 (422 nm),
LSTP-4 (421 nm)) > LSTP-2 (415 nm). These results agree with the
literature data that introduction of electron-withdrawing groups to
the pyridine ring can cause a decrease of the HOMO level and a
larger band gap than the unsubstituted one and vice versa. Fig. 2
shows the absorption spectra of LSTP-1eLSTP-7.
ꢁ
ꢀ
X-ray selected bond lengths (A) and angles ( ) around the metal core in the Pt(II)
complexes.
PteN
PteC
PteO
CePteN
OePteO
PtePt
LSTP-1
[39]
1.9954
1.9574
2.0943 (2.0013)
81.56
92.04
3.394
LSTP-2
LSTP-3
LSTP-4
LSTP-6
LSTP-7
1.8835
2.0574
1.9952
1.9956
2.0013
1.9889
1.9623
1.9699
1.9436
1.9722
2.1238 (2.0195)
2.1061 (1.9996)
2.0850 (1.9946)
2.0702 (1.9959)
2.1007 (2.0026)
85.51
81.27
81.98
81.95
82.21
91.20
88.57
92.12
92.19
92.26
2.843
3.865
3.483
4.904
4.571
diffraction studies. All of them can rapidly form microcrystalline
solids from solvent mixtures of trichloromethane and hexane.
Perspective drawings of Pt(II) complexes are shown in Fig. 1. And
key bonding parameters are given in Table 1. The PteN distance is
The room temperature phosphorescence spectra of LSTP-1e
LSTP-7 are depicted in Fig. 2. The colors of the complexes span from
green to yellow and orange (in the web version). Fig. 3 shows the
color-tuning strategy achieved by the modification of the pyridyl
ring of Pt(II) complexes with different substituents. The emission
spectra possess distinctive vibronic like progression, which we can
expect a significant amount of 3MLCT state mixing with the ligand-
ꢀ
1.883(5)e2.057(4) A, which is slightly longer than that of common
ꢀ
PteN bonds. The PteC distance is 1.943(6)e1.988(9) A. The CePteN
and OePteO angles are 81.27e85.51ꢁ and 88.57e92.26ꢁ, which are
similar to reported values [39]. The bond distance of the PteO edge
centered 3p
ep transitions. The emission energies are strongly
ꢀ
trans to C atom 2.070(2)e2.123(8) A is larger compared to that of
the other PteO bond 1.994(6)e2.019(5) A. Because the O atom trans
to C atom has a strong trans influence. The Pt$$$Pt distances in
LSTP-1, 2 and 4 are in the range of 2.7e3.5 A and thus a weak Pt$$$Pt
interaction are possible in the crystal. The Pt$$$Pt interaction don’t
exist in LSTP-3, 6 and 7. All other bond lengths around the Pt core
are typical for cyclometalates and b-diketonate derivatives of Pt(II)
[42e45].
ꢀ
sensitive to the electronic properties of substituents on the pyridyl
ring. A weakly donating methyl group at the 4-position of the
pyridyl ring results in a slight blue-shift of 7 nm for LSTP-2
comparing to LSTP-1. The emission is not influenced by the
methyl group in the 5- or 6-position at the pyridyl ring for LSTP-3
and LSTP-4. The stronger electron acceptor of trifluoromethyl group
at the 5-position on the pyridyl ring imparts a substantial red-shift
of 28 nm for LSTP-6, while the cyano group at the same position
imparts a more substantial red-shift up to 56 nm for LSTP-7. A
fluoro group in the 5-position causes a bathochromic shift of 9 nm
for LSTP-5. Therefore, lem decreases in the following order: LSTP-
7 > LSTP-6 > LSTP-5 > (LSTP-3, LSTP-4, LSTP-1) > LSTP-2.
We further probed the photophysical properties of LSTP-1e
LSTP-7 by measuring their PL quantum yields (Fp) in dilute
degassed CH2Cl2 solutions. Among all the green/yellow/orange (in
the web version) compounds, LSTP-4 has the highest room tem-
perature quantum efficiency of 19%, which is higher than that for its
isomeric compound LSTP-2 (9%) and LSTP-3 (4%). An increase in Fp
(16%) was observed when a trifluoromethyl group was attached to
the pyridine ring. As the energy of emission decreases, a corre-
sponding general decrease in Fp at room temperature is observed.
We propose that the red-shifted emission is due to the strong
electron-donating ability of the diphenylamine group.
ꢀ
3.2. Photophysical and thermal properties
Since good thermal stabilities of the compounds are very
important for applications, the onset decomposition temperatures
(Tdec) of the new compounds were determined from thermogra-
vimetric analysis (TGA) under a nitrogen stream. It is clear from the
onset of the TGA curves, all Pt(II) complexes exhibit high thermal
stability with their Tdec ranging from 230 to 320 ꢁC (Table 2). The
first weight loss of the compounds was mostly due to dissociation
of the ancillary acac ligand, which are necessary for high-
performance oxygen sensors.
The absorption and emission data of the Pt(II) complexes LSTP-
1eLSTP-7 are shown in Table 2. In common with all Pt(II) com-
plexes the absorption spectra can be divided into two regions: the
strong absorptions in the UV region (<350 nm) are derived from a
typical ligand-centered pe
p* transition because the corresponding
transitions were also observed in the free ligands. The second re-
gions that extend to the visible region are conventionally assigned
as mixing among singlet and triplet metal-to-ligand charge transfer
transitions (1MLCT and 3MLCT) and to a certain extent with intra-
3.3. Density functional theory (DFT) calculations
The structures of the complexes were optimized using density
functional theory (DFT) [46] with the B3LYP functional and
6-31G(d)/LanL2DZ basis set. The 6-31G(d) basis set was employed
ligand
pe
p* transitions through the spin-orbit coupling by the
Table 2
Photophysical and thermal data for the Pt(II) complexes.
s)c
Tdec (ꢁC)
b
Compound
Absorption (293 K)
Emission (293 K)
lem (nm) CH2Cl2
Fp
G
(m
labs (nm)a CH2Cl2
LSTP-1
LSTP-2
LSTP-3
LSTP-4
LSTP-5
LSTP-6
LSTP-7
256 (1.50), 307 (1.01), 333 (0.93), 424 (0.84)
257 (1.97), 307 (1.43), 415 (1.15)
540, 578sh
533, 572sh
542, 585sh
541, 580sh
549, 590sh
568
0.11
0.09
0.04
0.19
0.11
0.14
0.03
5.11
12.22
13.90
6.96
6.43
9.08
290 [30]
270
230
290
250
256 (1.90), 309 (1.48), 342 (1.46), 422 (1.10)
239 (1.43), 257 (1.44), 312 (0.91), 421 (0.69)
256 (1.84), 308 (1.19), 346 (1.18), 427 (0.70)
257 (2.17), 303 (1.23), 358 (1.03), 451 (1.47)
257 (2.38), 287 (1.70), 369 (0.99), 474 (2.30)
320
290
595
10.94
a
Extinction coefficients (104 Mꢀ1 cmꢀ1) are shown in parentheses.
b
c
Phosphorescence quantum yield in degassed dichloromethane. Measured in dichloromethane relative to [Ir(ppy)3] (UP ¼ 0.40), lex ¼ 400 nm.
In degassed dichloromethane, 25 ꢁC.

C. Liu et al. / Dyes and Pigments 101 (2014) 85e92
89
Fig. 2. (a) Absorption spectra and PL spectra of the Pt(II) complexes; c ¼ 1.0 ꢂ 10ꢀ5 mol dmꢀ3 in degassed dichloromethane. 25 ꢁC.
Fig. 3. Color-tuning strategy in cyclometalated Pt(II) complexes.
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 pack-
age [47]. To study the electronic structures and understand the
nature of excited states of our new Pt(II) phosphors, density
functional theory (DFT) calculations were carried out using B3LYP
hybrid functional theory for selected molecules. From Table 3, it is
clear that the HOMOeLUMO gaps calculated for LSTP-1eLSTP-4 are
close to each other, revealing that the HOMO and LUMO levels are
not influenced by a weakly
s-donating methyl group in the 6-
Table 3
position or 5-position on the pyridyl ring. In contrast, the HOMO
and LUMO levels are little influenced by the 4, 5, 6-methyl or 5-
fluoro on the pyridyl ring. Introducing an electron-withdrawing
cyano or trifluoromethyl group on the pyridine ring affects the
LUMO level significantly, resulting in a marked decrease in energy
gap.
Contour plots of dominant excitation orbitals of the Pt(II) complexes.
LSTP-1
LSTP-2
LSTP-3
LSTP-4
3.4. Electrochemical and electronic characterization
The electrochemical properties of LSTP-1eLSTP-7 were
examined using cyclic voltammetry, and the redox data are given
in Table 4. All of the electrochemical potentials reported here
were measured relative to an internal ferrocene standard (Cp2Fe/
Cp2Feþ) [48]. All Pt(II) complexes show reversible reduction and
irreversible oxidation waves. This electrochemical behavior is
LSTP-5
LSTP-6
LSTP-7
Table 4
Electrochemical properties and frontier orbital energy levels of the Pt(II) complexes.
Compound
HOMO (eV)a
LUMO (eV)b
Eg (eV)c
LSTP-1
LSTP-2
LSTP-3
LSTP-4
LSTP-5
LSTP-6
LSTP-7
ꢀ5.02
ꢀ4.91
ꢀ4.91
ꢀ5.05
ꢀ5.35
ꢀ5.39
ꢀ5.37
ꢀ1.73
ꢀ1.69
ꢀ1.73
ꢀ1.74
ꢀ2.25
ꢀ2.42
ꢀ2.51
3.29
3.22
3.18
3.31
3.10
2.97
2.86
a
0.1 M [Bu4N]PF6 in CH2Cl2, scan rate 100 mV sꢀ1, versus Fc/Fcþ couple.
b
c
LUMO ¼ HOMO þ Eg.
Estimated from the absorption edge (ledge) of solid films by equation of
Eg ¼ 1240/ledge
.

90
C. Liu et al. / Dyes and Pigments 101 (2014) 85e92
Fig. 4. Phosphorescent intensity response of sensing films of the complexes in IMPES-C to saturation O2/N2 cycles and small-step variations of O2 concentrations. (a) Saturation
switching emissive intensity response of sensing films of LSTP-3, LSTP-7 in IMPES-C to O2/N2 saturation cycles. (b) Dynamic emissive intensity response of sensing films of LSTP-3,
LSTP-7 in IMPES-C to O2/N2 saturation cycles, 25 ꢁC.
similar to that reported for related Pt(II) complexes [49]. Ac-
cording to the results in Tables 3 and 4, the LUMO level is pre-
dominantly pyridyl in character, while the HOMO level is mainly
influenced by the triphenylamine unit. This is mainly attributed
to the poorer electron-accepting property of triphenylamine as
compared to the phenyl ring. The results in Table 4 demonstrated
that the reduction potentials of these complexes are strongly
sensitive to the nature of substituents on the pyridyl ring. When
an electron-donating group (such as 4, 5, or 6-methyl group) is
attached to the pyridyl ring, the LUMO level is close to each
other. On the other hand, addition of an electron-withdrawing
substituent, such as cyano group (LSTP-7), fluorine (LSTP-5) or
trifluoromethyl group (LSTP-6), reduces the LUMO level. There-
fore, the LUMO level decreases in the order of LSTP-2
(ꢀ1.69 eV) > LSTP-1 (ꢀ1.73 eV), LSTP-3 (ꢀ1.73 eV), LSTP-4
(ꢀ1.74 eV) > LSTP-5 (ꢀ2.25 eV) > LSTP-6 (ꢀ2.42 eV) > LSTP-7
(ꢀ2.51 eV). This is in agreement with the results described in
literature [49e51] and a red-shift in the emission wavelength
often occurs when lowering the LUMO energy level.
Thus, the O2-sensing properties of the as-prepared complexes
were studied in polymer films (IMPES-C). Fig. 4 demonstrates the
phosphorescent intensity responses of sensing films of the com-
plexes LSTP-3 and LSTP-7 in IMPES-C to saturation O2/N2 cycles and
small-step variations of O2 concentrations.
The SterneVolmer quenching equation (Eq. (1)) is used to
quantitatively describe the luminescence O2 sensing [2].
Io
I
so
s
¼
¼ 1 þ kqso½Qꢃ
(1)
where Io stands for the emission intensity in inert atmosphere
(nitrogen for this study), I is the emission intensity under specific
As compared to Pt(ppy)acac (HOMO: ꢀ5.34 eV) [42], the HOMO
levels of LSTP-1eLSTP-7 are all elevated when the electron-rich
triphenylamine unit are attached to the pyridyl rings, signaling
that they have a lower ionization potential than ppy, leading to a
better hole-injection (HI) and/or hole-transporting (HT) ability.
3.5. Luminescent O2 sensing of the Pt(II) complexes in polymer films
For practical application of a metal complex as an indicator for
O2 sensing, the study of sensing films prepared by the distribution
of metal complexes in supporting polymers is more meaningful
than the study in a solution [2,16,52,53].
Fig. 5. Two-site model plots for the sensing films of the Pt(II) complexes in IMPES-C.
Intensity ratios I0/I versus O2 partial pressure.

C. Liu et al. / Dyes and Pigments 101 (2014) 85e92
91
Table 5
complexes. This is probably due to the conjugated effect of an
electron-withdrawing cyano (C^N) group on the 5-position of
pyridine ring. Although nitriles have attracted much attention due
to their potential applications in laser frequency doubling inte-
grated optics and optical communication [60,61], to the best of our
knowledge, the present result is the first example of a nitrile
compound used as a cyclometalating ligand for the O2 sensing.
Parameters for the O2-sensing film of the Pt(II) complexes with IMPES-C as the
supporting matrix (fitting of the results to the two-site model).
r2 c
K
pO2
a
a
b
b
app d
e
lex
lem
f01
f02
KSV1
KSV2
SV
(nm) (nm)
LSTP-1 425 542 0.7509 0.2491 0.0761 0.000 0.971 0.05714 23.4
LSTP-2 420 533 0.7673 0.2327 0.1069 0.000 0.936 0.08202 17.9
LSTP-3 425 542 0.7840 0.2160 0.0647 0.000 0.931 0.05072 26.6
LSTP-4 425 541 0.8067 0.1933 0.0713 0.001 0.935 0.05752 24.6
LSTP-5 430 549 0.7955 0.2045 0.0871 0.001 0.907 0.06929 21.9
LSTP-6 455 569 0.8074 0.1926 0.0833 0.000 0.913 0.06726 22.6
4. Conclusions
LSTP-7 475 596 0.8616 0.1384 0.1180 0.001 0.966 0.10167
9.7
In summary, a series of luminescent Pt(II) complexes featuring
functionalized hole-transporting TPA-based ligands were synthe-
sized and fully characterized. The structureeproperty relationships
were studied systematically. All complexes exhibit intense ab-
sorption bands with lmax in a range of 533e596 nm. The HOMO and
LUMO levels are little influenced by a methyl group at the 4, 5, 6-
position or a fluoro group at the 5-position of the pyridyl ring.
Introducing an electron-withdrawing group like cyano or tri-
fluoromethyl group on the pyridine ring affects the LUMO level
significantly, resulting in a marked decrease in energy gap and thus
red-shifted emission. All complexes exhibited intense phospho-
rescence emissions at room temperature. These neutral and air-
stable complexes were easily prepared, rendering good potential
in luminescence oxygen sensors. Among them the complex LSTP-7
demonstrated the highest sensitivity toward the oxygen sensing,
which is the first example of a nitrile compound used as a cyclo-
metalating ligand for the efficient O2 sensing. The present results
disclose the color-tuning strategy for the design of novel Pt(II)
complexes with good photoelectric performances for O2 sensing.
a
Ratio of the two portions of the Pt(II) complexes.
Quenching constants of the two portions.
b
c
Determination coefficients.
Weighted quenching constant, K
d
e
app
¼ f01KSV1 þ f02KSV2
.
SV
The oxygen partial pressure at which the initial emission intensity of the film is
quenched by 50% and calculated as 1/KSV, in Torr.
O2 partial pressure, kq is the quenching constant, so is the
unquenched lifetime and [Q] is the concentration of the quencher.
For heterogenous O2-sensing films, a modified SterneVolmer or
a two-site model is required to study the quenching effect [7,54]. In
the two-site model, the O2-sensitive complexes are considered as
two different portions. Because even in “homogeneous” polymers,
the complexes still dwell in different microenvironments [40,52].
The fraction of the two portions are defined as f01 and f02, respec-
tively (f01 þ f02 ¼ 1); the two portions have different quenching
constants (KSV1 and KSV2); see Eq. (2).
ꢀ
ꢁꢀ1
Io
I
f01
f02
¼
þ
(2)
1 þ KSV1½O2ꢃ 1 þ KSV2½O2ꢃ
Acknowledgment
With the home-assembled flow cell coupled to a spectrofluo-
The authors thank the financial support from the National
Natural Science Foundation of China (21276043), and the Ministry
of Education (the Program for New Century Excellent Talents in
University).
rimeter, the responses of the sensing films to different O2 partial
pressure were studied (Fig. 4). First the O2-sensing films of LSTP-3
and LSTP-7 were tested against the saturation cycle of O2 and N2
(Fig. 4, LSTP-3a and LSTP-7a) (others see the Supporting
information). The films in N2 exhibit intense emission, but the
phosphorescence is substantially quenched in O2. Furthermore, fast
response (t Y 90) and recovery times (t [ 90) of 5e10 s and 20e30 s
were observed, respectively [15,54]. The response (t Y 90) and re-
covery times (t [ 90) are generally accepted as the times for
luminescence intensity changes to reach 90% of the whole variation
when switching from 100% N2 to 100% O2 or vice versa. Fast
response times are usually observed for porous supporting mate-
rials such as MCM-41 molecularsieves [19,55e59]. Next, the dy-
namic response of the O2-sensing films was tested against small
steps of O2 partial pressure variation (Fig. 4. LSTP-3b and LSTP-7b)
(others see the Supporting information). Such a detailed study will
reveal the dynamic O2 partial pressure range and the data can be
used to evaluate the O2 sensitivity. We found that the sensing film
with LSTP-7 is more sensitive to O2 than others. For example, the
emission intensity of LSTP-7 was quenched by 69.7% under 3.5% O2.
For others, however, the emission is quenched by only around (54e
60)% in the presence of 5% O2. To compare the O2-sensing proper-
ties of the complexes quantitatively, the O2-sensing data were fitted
to the two-site model (Fig. 5) and the results are summarized in
Table 5. The KaSpVp value is not influenced by a methyl group in the 5-
position or 6-position on the pyridyl ring comparing to LSTP-1,
while the methyl group in the 4-position of the pyridyl ring
resulted in a relative higher KaSpVp value. Complexes with a fluoro or
trifluoromethyl group at the 5-position of the pyridyl ring provided
a little higher KaSpVp value than that of the LSTP-1. It is clear that the
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2013.09.030.
References
[1] Ishiji T, Kaneko M. Photoluminescence of pyrenebutyric acid incorporated into
silicone film as
a technique in luminescent oxygen sensing. Analyst
1995;120(6):1633.
[2] Lakowicz JR. Principles of fluorescence spectroscopy. 2nd ed. New York:
Kluwer Academic/Plenum Publishers; 1999.
[3] Gray JM, Karow DS, Lu H, Chang AJ, Chang JS, Ellis RE, et al. Oxygen sensation
and social feeding mediated by a C. elegans guanylate cyclase homologue.
Nature 2004;430(6997):317e22.
[4] Wolfbeis OS. Sensor paints. Adv Mater 2008;20(19):3759e63.
[5] Higgins C, Wencel D, Burke CS, MacCraith BD, McDonagh C. Novel
hybrid optical sensor materials for in-breath O(2) analysis. Analyst
2008;133(2):241e7.
[6] Persson A, Gross E, Laurent P, Busch KE, Bretes H, de Bono M. Natural variation
in a neural globin tunes oxygen sensing in wild Caenorhabditis elegans. Nature
2009;458(7241):1030e3.
[7] Wang Z, Chen T, Xu J. Gas and water vapor transport through a series of novel
poly(aryl ether sulfone) membranes. Macromolecules 2001;34(26):9015e22.
[8] Quaranta M, Borisov SM, Klimant I. Indicators for optical oxygen sensors.
Bioanal Rev 2012;4(2e4):115e57.
[9] Amao Y. Probes and polymers for optical sensing of oxygen. Microchim Acta
2003;143(1):1e12.
[10] Lu X, Winnik MA. Luminescence quenching in polymer/filler nanocomposite
films used in oxygen sensors. Chem Mater 2001;13(10):3449e63.
[11] Huynh L, Wang Z, Yang J, Stoeva V, Lough A, Manners I, et al. Evaluation of
phosphorescent rhenium and iridium complexes in polythionylphosphazene
films for oxygen sensor applications. Chem Mater 2005;17(19):4765e73.
quenching constant (the sensitivity toward O2) of LSTP-7
app
(K
¼ 0.102 Torrꢀ1) is much higher than those of other Pt(II)
SV

92
C. Liu et al. / Dyes and Pigments 101 (2014) 85e92
[12] Han B-H, Manners I, Winnik MA. Oxygen sensors based on mesoporous silica
particles on layer-by-layer self-assembled films. Chem Mater 2005;17(12):
3160e71.
[37] Jou JH, Chen CC, Chung YC, Hsu MF, Wu CH, Shen SM, et al. Nanodot-enhanced
high-efficiency pure-white organic light-emitting diodes with mixed-host
structures. Adv Funct Mater 2008;18(1):121e6.
[13] Vanderkooi JM, Wilson DF. Oxygen transport to tissue VIII. In: Langmuir IS,
editor. New York: Plenum; 1986. p. 189.
[14] Amao Y, Ishikawa Y, Okura I. Green luminescent iridium(III) complex immo-
bilized in fluoropolymer film as optical oxygen-sensing material. Anal Chim
Acta 2001;445(2):177e82.
[15] Ji S, Wu W, Wu W, Song P, Han K, Wang Z, et al. Tuning the luminescence
lifetimes of ruthenium(ii) polypyridine complexes and its application in
luminescent oxygen sensing. J Mater Chem 2010;20(10):1953.
[16] Wu W, Cheng C, Wu W, Guo H, Ji S, Song P, et al. Tuning the emission colour of
triphenylamine-capped cyclometallated platinum(II) complexes and their
application in luminescent oxygen sensing and organic light-emitting diodes.
Eur J Inorg Chem 2010;29:4683e96.
[38] Tamoto N, Adachi C, Nagai K. Electroluminescence of 1,3,4-oxadiazole and
triphenylamine-containing molecules as an emitter in organic multilayer light
emitting diodes. Chem Mater 1997;9(5):1077e85.
[39] He Z, Wong W-Y, Yu X, Kwok H-S, Lin Z. Phosphorescent platinum(II) com-
plexes derived from multifunctional chromophores: synthesis, structures,
photophysics, and electroluminescence. Inorg Chem 2006;45(26):10922e37.
[40] Mak CSK, Pentlehner D, Stich M, Wolfbeis OS, Chan WK, Yersin H. Exceptional
oxygen sensing capabilities and triplet state properties of Ir(ppy-NPh2)3.
Chem Mater 2009;21(11):2173e5.
[41] Liu C, Rao X, Song X, Qiu J, Jin Z. Palladium-catalyzed ligand-free and aqueous
Suzuki reaction for the construction of (hetero)aryl-substituted triphenyl-
amine derivatives. RSC Adv 2013;3(2):526e31.
[17] Wolfbeis O, Leiner MP, Posch H. A new sensing material for optical oxygen
measurement, with the indicator embedded in an aqueous phase. Microchim
Acta 1986;90(5e6):359e66.
[42] Brooks J, Babayan Y, Lamansky S, Djurovich PI, Tsyba I, Bau R, et al. Synthesis
and characterization of phosphorescent cyclometalated platinum complexes.
Inorg Chem 2002;41(12):3055e66.
[18] Di Marco G, Lanza M, Pieruccini M, Campagna S. A luminescent iridium(III)
cyclometallated complex immobilized in a polymeric matrix as a solid-state
oxygen sensor. Adv Mater 1996;8(7):576e80.
[43] Ma B, Li J, Djurovich PI, Yousufuddin M, Bau R, Thompson ME. Synthetic
control of Pt/Pt separation and photophysics of binuclear platinum com-
plexes. J Am Chem Soc 2004;127(1):28e9.
[19] Zhang H, Sun Y, Ye K, Zhang P, Wang Y. Oxygen sensing materials based on
mesoporous silica MCM-41 and Pt(II)eporphyrin complexes. J Mater Chem
2005;15(31):3181e6.
[44] Chassot L, Mueller E, Von Zelewsky A. cis-Bis(2-phenylpyridine)platinum(II)
(CBPPP): a simple molecular platinum compound. Inorg Chem 1984;23(25):
4249e53.
[20] Ma B, Djurovich PI, Garon S, Alleyne B, Thompson ME. Platinum binuclear
complexes as phosphorescent dopants for monochromatic and white organic
light-emitting diodes. Adv Funct Mater 2006;16(18):2438e46.
[21] Suzuki S, Sugimura R, Kozaki M, Keyaki K, Nozaki K, Ikeda N, et al. Highly
efficient photoproduction of charge-separated states in donoreacceptor-
linked bis(acetylide) platinum complexes. J Am Chem Soc 2009;131(30):
10374e5.
[45] Laskar IR, Hsu S-F, Chen T-M. Highly efficient orange-emitting OLEDs based on
phosphorescent platinum(II) complexes. Polyhedron 2005;24(8):881e8.
[46] Hohenberg P, Kohn W. Inhomogeneous electron gas. Phys Rev 1964;136(3B):
B864e71.
[47] Frisch MJTG, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR. Gaussian 09.
Revision A.1. Wallingford, CT: Gaussian Inc.; 2009.
[48] Pommerehne J, Vestweber H, Guss W, Mahrt RF, Bässler H, Porsch M, et al.
Efficient two layer leds on a polymer blend basis. Adv Mater 1995;7(6):
551e4.
[22] Zhao Q, Li F, Huang C. Phosphorescent chemosensors based on heavy-metal
complexes. Chem Soc Rev 2010;39(8):3007e30.
[23] Wu W, Xu X, Yang H, Hua J, Zhang X, Zhang L, et al. De
p
eMe
p
eA structured
[49] Zhou G, Wang Q, Wang X, Ho C-L, Wong W-Y, Ma D, et al. Metallophosphors
of platinum with distinct main-group elements: a versatile approach towards
color tuning and white-light emission with superior efficiency/color quality/
brightness trade-offs. J Mater Chem 2010;20(35):7472.
platinum acetylide sensitizer for dye-sensitized solar cells. J Mater Chem
2011;21(29):10666.
[24] Wu W, Zhang J, Yang H, Jin B, Hu Y, Hua J, et al. Narrowing band gap of
platinum acetylide dye-sensitized solar cell sensitizers with thiophene
bridges. J Mater Chem 2012;22(12):5382.
[25] Xu XD, Zhang J, Yu X, Chen LJ, Wang DX, Yi T, et al. Design and preparation of
platinumeacetylide organogelators containing ethynyl-pyrene moieties as
the main skeleton. Chem Eur J 2012;18(50):16000e13.
[26] Jiang B, Chen LJ, Xu L, Liu SY, Yang HB. A series of new star-shaped or
branched platinumeacetylide derivatives: synthesis, characterization, and
their aggregation behavior. Chem Commun 2013;49(62):6977e9.
[27] Li ZY, Xu L, Wang CH, Zhao XL, Yang HB. Novel platinumeacetylide metallo-
cycles constructed via a stepwise fragment coupling approach and their ag-
gregation behaviour. Chem Commun 2013;49(55):6194e6.
[28] Xu XD, Zhang J, Chen LJ, Zhao XL, Wang DX, Yang HB. Large-scale honeycomb
microstructures constructed by platinumeacetylide gelators through supra-
molecular self-assembly. Chem Eur J 2012;18(6):1659e67.
[29] Papkovskii DB, Yaropolov AI, Savitskii AP, Olah J, Rumyantseva VD,
Mironov AF, et al. Fibre-optic oxygen sensor based on phosphorescence
quenching. Biomed Sci 1991;2(5):536e9.
[30] Xiang H, Zhou L, Feng Y, Cheng J, Wu D, Zhou X. Tunable fluorescent/phos-
phorescent platinum(II) porphyrinefluorene copolymers for ratiometric dual
emissive oxygen sensing. Inorg Chem 2012;51(9):5208e12.
[31] Papkovsky DB, Ponomarev GV, Trettnak W, O’Leary P. Phosphorescent com-
plexes of porphyrin ketones: optical properties and application to oxygen
sensing. Anal Chem 1995;67(22):4112e7.
[32] Papkovsky DB, O’Riordan TC. Emerging applications of phosphorescent met-
alloporphyrins. J Fluoresc 2005;15(4):569e84.
p
-
[50] Grushin VV, Herron N, LeCloux DD, Marshall WJ, Petrov VA, Wang Y. New,
efficient electroluminescent materials based on organometallic Ir complexes.
Chem Commun (Camb) 2001;(16):1494e5.
[51] Tsuboyama A, Iwawaki H, Furugori M, Mukaide T, Kamatani J, Igawa S, et al.
Homoleptic cyclometalated iridium complexes with highly efficient red
phosphorescence and application to organic light-emitting diode. J Am Chem
Soc 2003;125(42):12971e9.
[52] Wolfbeis O, Narayanaswamy R. Optical sensors: industrial, environmental and
diagnostic applications. Berlin, Heidelberg: Springer; 2004.
[53] Wang Z, Chen T, Xu J. Gas transport properties of novel cardo poly(aryl
ether ketone)s with pendant alkyl groups. Macromolecules 2000;33(15):
5672e9.
[54] Ji S, Wu W, Wu Y, Zhao T, Zhou F, Yang Y, et al. Real-time monitoring of
luminescent lifetime changes of PtOEP oxygen sensing film with LED/
photodiode-based time-domain lifetime device. Analyst 2009;134(5):958e65.
[55] Leventis N, Rawashdeh A-MM, Elder IA, Yang J, Dass A, Sotiriou-Leventis C.
Synthesis and characterization of Ru(II) tris(1,10-phenanthroline)-electron
acceptor dyads incorporating the 4-benzoyl-N-methylpyridinium cation or N-
benzyl-N0-methyl viologen. Improving the dynamic range, sensitivity, and
response time of solegel-based optical oxygen sensors. Chem Mater
2004;16(8):1493e506.
[56] Yeh T-S, Chu C-S, Lo Y-L. Highly sensitive optical fiber oxygen sensor using
Pt(II) complex embedded in solegel matrices. Sens Actuators B 2006;119(2):
701e7.
[57] Basu BJ. Optical oxygen sensing based on luminescence quenching of plat-
[33] Wu W, Guo H, Wu W, Ji S, Zhao J. Long-lived room temperature deep-red/
near-IR emissive intraligand triplet excited state (3IL) of naphthalimide in
cyclometalated platinum(II) complexes and its application in upconversion.
Inorg Chem 2011;50(22):11446e60.
inum porphyrin dyes doped in ormosil coatings. Sens Actuators B
2007;123(1):568e77.
[58] Wang B, Liu Y, Li B, Yue S, Li W. Optical oxygen sensing materials based on
trinuclear starburst ruthenium(II) complexes assembled in mesoporous silica.
J Lumin 2008;128(3):341e7.
[34] Wang J, He C, Wu P, Wang J, Duan C. An amide-containing metaleorganic
tetrahedron responding to
enhancement manner for biological imaging of no in living cells. J Am Chem
Soc 2011;133(32):12402e5.
a
spin-trapping reaction in
a
fluorescent
[59] Zhou G-J, Wang Q, Wong W-Y, Ma D, Wang L, Lin Z. A versatile color tuning
strategy for iridium(III) and platinum(II) electrophosphors by shifting the
charge-transfer states with an electron-deficient core.
2009;19(13):1872e83.
J Mater Chem
[35] Liang M, Xu W, Cai F, Chen P, Peng B, Chen J, et al. New triphenylamine-based
organic dyes for efficient dye-sensitized solar cells.
2007;111(11):4465e72.
J
Phys Chem
C
[60] Brown HC, Okamoto Y. Electrophilic substituent constants. J Am Chem Soc
1958;80(18):4979e87.
[36] Su YZ, Lin JT, Tao Y-T, Ko C-W, Lin S-C, Sun S-S. Amorphous 2,3-substituted
thiophenes: potential electroluminescent materials. Chem Mater
2002;14(4):1884e90.
[61] Edelstein L, Stetz MA, McMahon HA, Londergan CH. The effects of a-helical
structure and cyanylated cysteine on each other. J Phys Chem B 2010;114(14):
4931e6.