Tuning the emission properties of cyclometalated platinum(II) complexes by intramolecular electron-sink/arylethynylated ligands and its application for enhanced luminescent oxygen sensing

Article abstract of DOI:10.1039/c0jm01794a

We have synthesized five novel cyclometalated Pt(II) complexes (aryl-ppy)Pt(acac) (ppy = 2-phenyl pyridine, aryl = N-butyl naphthalimide (NI) ethynylene for Pt-1, N-butyl naphthalimide (NI)-CH₂ -CO- for Pt-2, 4-cyanophenyl - CH₂ - CO

Full text of DOI:10.1039/c0jm01794a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Tuning the emission properties of cyclometalated platinum(II) complexes by
intramolecular electron-sink/arylethynylated ligands and its application for
enhanced luminescent oxygen sensing†
Wanhua Wu,a Wenting Wu,a Shaomin Ji,a Huimin Guo,b Peng Song,c Keli Han,c Lina Chi,a Jingyin Shaoa
a
*
and Jianzhang Zhao
Received 7th June 2010, Accepted 26th July 2010
DOI: 10.1039/c0jm01794a
We have synthesized five novel cyclometalated Pt(II) complexes (aryl-ppy)Pt(acac) (ppy ¼ 2-phenyl
pyridine, aryl ¼ N-butyl naphthalimide (NI) ethynylene for Pt-1, N-butyl naphthalimide (NI)–CH2
–CO– for Pt-2, 4-cyanophenyl – CH2 – CO– for Pt-3, naphthal ethynylene for Pt-4 and naphthal-diketo
for Pt-5). For the first time, p-conjugation of the ppy ligands was extended via the C^C bond. Deep
red/near IR emission (638 nm–700 nm) was observed for the complex containing naphthalimide
ethynylene subunit (Pt-1), whereas the close analogue Pt-2 (in which the linker between the NI and the
ppy subunit is a –CH2CO– group) shows a relatively blue-shifted emission (540 nm–570 nm) but much
longer luminescent lifetime (s ¼ 25.5 ms) than Pt-1 (s ¼ 6.6 ms). Simultaneous fluorescence/
phosphorescence emissions were observed for Pt-1 and Pt-2, but other complexes show sole
phosphorescent emission. The red-shifted phosphorescence of the complexes compared to the model
complex ppyPt(acac) (486 nm) was attributed to either the significant electron-sink effect of the NI
fragment (Pt-1) (for which the electron withdrawing effect is stronger than the previously reported
fluoren-9-one), or the extended p-conjugation of the ppy ligand (via C^C bond) (e.g. Pt-4). The
substantial tuning of the emission color and the luminescent lifetimes (0.86 ms–25.5 ms) of the complexes
were rationalized by theoretical calculations (DFT/TDDFT), i.e. the emissive triplet excited states were
3
assigned as the normal 3MLCT state (give smaller s values) or the novel ligand-localized IL emissive
state (give larger s values). With tuning the luminescent lifetimes, the luminescent O2 sensitivity of the
complexes was improved by 117-fold (Stern–Volmer quenching constants KSV ¼ 0.234 Torrꢀ1 for Pt-2
vs. KSV ¼ 0.002 Torrꢀ1 for Pt-5).
groups to the pyridine group of the ppy moiety (where the
Introduction
LUMO is localized), thus the energy gap between the HOMO
and LUMO will be decreased and a red-shifted emission will be
observed.4 However, this methodology shows limited capability
to tune the emission wavelength.4 Alternatively the ppy ligand is
substituted with heterocyclic compounds, such as coumarin etc.,
to tune the emission wavelength.4,8
Cyclometalated Pt(II)/Ir(III) complexes have attracted much
attention due to their applications as phosphorescent emitters in
organic light emitting diodes (OLEDs).1–22 The emissive excited
state of these complexes are intra-ligand or metal-to-ligand-
charge-transfer triplet states (3IL/3MLCT). Concerning the
application for OLEDs, one of the critical issues is to tune the
emission color of the complexes.5 To this end, the routine
molecular tailoring approach is to attach electron-donating
substituents on the phenyl group of the 2-phenylpyridine (ppy)
ligand (where HOMO is localized), or electron-withdrawing
Recently we have been interested in luminescent transition
metal complexes and the exploration of their potential to be used
as molecular sensing materials, such as O2 sensors.23,24 Most of
the O2 sensors are based on the quenching of the phosphores-
cence of transition metal complexes by O2, such as Ru(II) poly-
imine complexes (luminescent lifetime s in ms range), etc.6,7,23–25
The ideal lumophores, however, will be those that show longer s
values, which lead to higher sensitivity.23,24 The lifetimes of
Ru(II) polyimine complexes can be tuned with the introduction
of specific organic chromophores, such as pyrene.24a Recently
cyclometalated Ir(III) complexes have been used for O2 sensing.25
However, very few efforts have been made to tune the emission
lifetimes of the cyclometalated Pt(II)/Ir(III) complexes. More-
over, lumophores that show simultaneous fluorescence/phos-
phorescence dual emission will have more potential when used as
O2 sensing materials.22,23 This kind of signal transduction for O2
sensing is superior to the emission intensity-based sensors, which
aState Key Laboratory of Fine Chemicals, School of Chemical Engineering,
Dalian University of Technology, P.O. Box 40, 158 Zhongshan Road,
Dalian, 116012, P. R. China. E-mail: zhaojzh@dlut.edu.cn; Fax: + 86
411 3960 8007; Tel: + 86 411 3960 8007
bDepartment of Chemistry, School of Chemical Engineering, Dalian
University of Technology, P.O. Box 40, 158 Zhongshan Road, Dalian,
116012, P. R. China
cDalian Institute of Chemical Physics, Chinese Academy of Sciences, 457
Zhongshan Road, Dalian, 116023, P. R. China
† Electronic Supplementary Information (ESI) available: General
procedures, synthesis methods and 1H, 13C NMR and MS spectra of
the complexes, oxygen quenching studies of the complexes. CCDC
reference numbers 762731 and 762732. See DOI: 10.1039/c0jm01794a/.
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ꢀ
bond lengths are in the range 2.006–2.092 A. The C(7)–Pt(1)
is liable to be affected by many experimental uncertainties, such
as the photobleaching of the dyes, the drifting of the excitation
power, etc.6,7,22,26,27
ꢀ
bond length is 1.877 A, which is slightly shorter than the typical
C–Pt bond length.19 The N(1)–Pt(1) bond length is 1.991 A. The
ꢀ
Inspired by the aforementioned challenge as well as the recent
progress of cyclometalated Pt(II) complexes and the O2 sensing
materials,8,12,14,19,20,22,28 herein we set out to explore new strategies
to tune the emission color of cyclometalated complexes by
changing the electronic structure of the excited states with an
intramolecular electron sink,5d and to study the applications of
these phosphorescent materials for luminescent O2 sensing.
Herein we synthesized five new cyclometalated Pt (II)
complexes with arylethynylene subunits on the ppy ligands.5 To
the best of our knowledge, this is the first time that ethynylated
ligands (–C^C–) were used to extend the p-conjugation of the
ppy ligands of cyclometalated Pt(II) complexes.4 We used an
electron sink to tune the emission color of the complexes. It
should be pointed out that reports on tuning the emission color
of cyclometalated Pt complexes with an electron-sink are limit-
ed,5d thus leaving much room for further investigation. In the
metallation procedure of the ethynylene ligands, oxidization of
the ethynylene to keto structure was found, and unexpected
mono-keto or diketo side-products were isolated. Pt-1
(NI subunit attached to ppy via –C^C– group) shows deep red/
near IR emission, which is red-shifted by ca. 150 nm compared to
the model complex ppyPt(acac). Interestingly, for the complex
with NI attached to the ppy ligand via a methylene-keto group
(Pt-2), blue-shifted emission at 538 nm and long luminescent
lifetime (s ¼ 25.5 ms) were observed. For Pt-4, in which the
naphthalene subunit was attached to ppy, emission at 575 nm was
observed. We found that the luminescent O2 sensing of the
complexes can be improved by 117-fold with tuning the lumi-
nescent lifetimes, these results show substantial improvement
compared to recently reported cyclometalated Ir(III) complexes
(for O2 sensing),25 e.g. the new complex Pt-2 shows 66-fold
higher oxygen sensitivity than the recently reported Ir(III)
complex.25
coordination angles, O(2)–Pt(1)–O(1) and C(7)–Pt(1)–N(1), are
91.8ꢁ and 80.4ꢁ, respectively, which are close to the typical Pt(II)
coordination geometries.19 No PtII/PtII interaction was found in
the crystal structure.
A trans skewed geometry was found for the a-diketo moiety of
Pt-5, with a torsion angle of O(4)–C(18)–C(17)–O(3) ¼ 85.2ꢁ,
which is in agreement with a-diketo compounds (Fig. 1b).33
Coordination angles O(2)–Pt(1)–O(1) and C(6)–Pt(1)–N(1) are
92.3ꢁ and 81.8ꢁ, respectively. The O–Pt bond lengths are in the
ꢀ
range 1.974–2.071 A. The C(6)–Pt(1) and N(1)–Pt(1) bond
ꢀ
ꢀ
lengths are 1.937 A and 1.970 A, respectively. Similar to Pt-1,
there is no significant Pt(II)/Pt(II) interaction in the crystal
structure of Pt-5.
Photophysical properties
For L-2 and L-3, the UV-vis absorption bands are centered in the
UV range (Fig. 2). For L-1, however, strong absorption in the
visible region was observed. These absorptions are due to
the p–p* transitions of the chromophores.
With metallation, new absorption bands at lower energy
1
(ca. 400 nm) developed, which are due to the S0 / MLCT
transition. The molar extinction coefficients (3 ¼ 0.41–3.4 ꢂ
1
104 cmꢀ1 molꢀ1 dm3) are in agreement with the MLCT absorp-
tion feature of the ppyPt (acac) complexes.4,5,8 The intense
absorptions in the UV range are due to the ligand centered 1p–p*
transitions. These assignments were supported by our TDDFT
calculations.
For Pt-1, intensive absorption in the visible range was observed
(beyond 400 nm), with 3 up to 33700 cmꢀ1 molꢀ1 dm3. We propose
1
the MLCT absorption bands (as a shoulder at 430 nm) are
buried in the intensive absorption band of NI p–p* transitions,
which is supported by the TDDFT calculations (ESI†). The high
3 value of Pt-1 in the visible range is beneficial for further lumi-
nescent biosensing or bioimaging applications.34–40
Results and discussion
Emission at 575 nm was observed for Pt-4, which isred-shifted by
ca. 100 nm vs. ppyPt(acac) (486 nm) (Fig. 3c).8 The emission is
substantially quenched in air (reduced to 97.2% compared to that in
N2), which indicates a long luminescent lifetime (s ¼ 15.8 ms).6,23,24
To the best of our knowledge, this is the first report of tuning
the emission color of cyclometalated Pt(II) complexes with
extension of the p-conjugation of a ppy ligand via C^C triple
bonds (by Sonogashira coupling reaction, a well-established
organic synthetic methodology). This approach can be general-
ized to prepare novel cyclometalated Pt(II) complexes to tune the
emission properties of the complexes.
Synthesis
4-Bromo-phenylpyridine was prepared with pyridine and
4-bromobenzeneamine (Scheme 1).29 The arylethynylated ppy
ligands were prepared by Pd catalyzed Sonogashira coupling
reactions. It should be pointed out that more functionalized NI
moieties can be prepared readily, e.g. simply by using function-
alized amines.30,31 During the metalation of the ethylnylated
ligands with K2PtCl4, complexes with keto groups (Pt-2, Pt-3
and Pt-5) were obtained, due to the Pt(II) catalyzed oxidation of
the C^C bonds.32 All the complexes were obtained in satisfying
yields.
However, extension of the p-conjugation of the ppy ligand
does not necessarily guarantee luminescence. For example,
a
cyclometalated Pt(II) complex with an arylethylene
Crystal structures of complexes containing ethynyl and a-diketo
(C]C double bonds) modified ppy ligand is non-luminescent,41
probably due to the significant cis/trans isomerization of the
C]C double bonds, as a result the luminescence is completely
quenched. In our case C^C triple bonds are rigid and an ideal
conjugated linker for efficient through-bond energy transfer, i.e.
electronic communication between the fluorophores at both ends
of the C^C bonds.34,36,42,43
linker: Pt-1 and Pt-5
For Pt-1, the ethynylene linker is distorted, the C9–C12–C13
bond angle is 171.2ꢁ (Fig. 1). The NI moiety takes a coplanar
geometry with the ppy moiety, and ensures efficient electronic
communication between the two parts. A distorted square planar
geometry was found for the Pt coordination center. The O–Pt
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Scheme 1 Synthesis of the cyclometalated Pt complexes Pt-1, Pt-2, Pt-3, Pt-4 and Pt-5. The structures of the parent complex ppyPt(acac) and the
polymer diisopropyl substituted cardo poly(aryl ether ketone) (IMPEK – C) are also shown. (a) n-Butylamine, ethanol, 60 ꢁC, 6 h; (b) trimethylsily-
lacetylene, Pd(PPh3)4, CuI, NEt3, reflux, 8 h; (c) Bu4NF, THF, rt; (d) Pd(PPh3)2Cl2, PPh3, CuI, NEt3, ethanol, 60 ꢁC, 6 h; (e) K2PtCl4, 2-ethoxyethanol/
water ¼ 3 : 1 (v/v), 80 ꢁC; (f) Hacac, Na2CO3, 2-ethoxyethanol, 100 ꢁC; (g) NaNO2, HCl, KI, 0–5 ꢁC; (h) 2-(40-bromophenyl) pyridine, Pd(PPh3)4, NEt3,
ethanol, 60 ꢁC, 6 h; (i) 2-(40-bromophenyl) pyridine, Pd(PPh3)4, toluene, (i-Pr)2NH, reflux, 8 h.
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respectively (Fig. 4). It should be pointed out that the emission of
Pt-5 are against the traditional photophysics of the cyclo-
metalated complexes, i.e. blue-shifted emission will be expected if
an electron-withdrawing moiety is attached to the phenyl group
of the ppy ligand, where the HOMO is localized.4
Compared to Pt-4 (lem ¼ 575 nm), emission at 638 nm was
observed for Pt-1, the Stokes shift is up to 248 nm. The struc-
tured emission band, large Stokes shift and long luminescent
lifetime (6.6 ms) indicate the phosphorescence feature of the
emission. Notably the emission wavelength is red-shifted by ca.
152 nm compared to ppyPt(acac).8 The red-shifted emission of
Pt-1 is also unexpected,8 which infers that the emissive state is
different from the normal ppyPt(acac) complexes. DFT/TDDFT
3
calculations indicate that the IL/3MLCT excited state with ppy
/ NI electron transfer is responsible for the red-shifted emission
of Pt-1, i.e. the NI moiety serves as an electron-sink (electron
acceptor) in the excited state. We noticed the NI moiety is
a stronger electron sink than the previously reported fluoren-9-
one because the emission of Pt-1 is more red-shifted and the
luminescent lifetime of Pt-1 is longer.5d
Interestingly, besides the major emission at 638 nm, minor
emission bands at 455 nm and 530 nm were also observed for
Pt-1. The structureless feature, the small Stokes shift (65 nm) and
the short luminescence lifetime (3.2 ns) attribute the emission at
455 nm to fluorescence. The emission at 530 nm is sensitive to O2,
thus we attribute this emission band to the normal triplet 3MLCT
state. This kind of uni-chromophore fluorescence/phosphores-
cence dual emission is rare for cyclometalated Pt/Ir
complexes.4,19,44 We noticed that the decomposition of Pt-1 gives
similar emission at ca. 450 nm (possibly due to the emission of the
free ligand). The emission of Pt-1 and Pt-2 were studied imme-
diately after column purification and the purity of the complexes
was checked by HPLC (see ESI†).
Fig. 1 ORTEP drawing of the complexes (a) Pt-1 and (b) Pt-5 with
thermal ellipsoids shown at the 50% probability level. All H atoms are
omitted for clarity.
The –C^C– triple bond in Pt-2 is oxidized to a keto structure,
thus the p-conjugation in the ligand is disrupted. Emission at
538 nm was found for Pt-2, vs. 638 nm of Pt-1. We attribute the
3
emission at 538 nm to the normal MLCT emissive state. The
blue-shifted emission of Pt-2 compared to Pt-1 indicates that the
p-conjugated NI-ppy fragment is necessary for the red-shifted
emission in the red/near IR range. A minor fluorescence emission
band at 386 nm was found for Pt-2. Thus, fluorescence/phos-
phorescence dual emission was observed for Pt-2. The dual
emission of the complexes were used for ratiometric luminescent
oxygen sensing, since the fluorescence emission is not sensitive to
oxygen but the phosphorescence is (see ESI†). We attribute the
dual emission of Pt-2 to its isolated fluorophore and phosphore,
which may lead to non-efficient ISC. The structural analogue Pt-
3 gives only phosphorescence emission.
The effect of the aryl-ethynyls, i.e. the NI moiety, the extended
p-conjugation and the a-diketo group, on the energy level of the
HOMO and LUMO orbitals is summarized (Fig. 4).
Fig. 2 UV-Vis absorption spectra of (a) the ligands L-1, L-2 and L-3 and
(b) the complexes Pt-1, Pt-2, Pt-3, Pt-4, Pt-5. 1.0 ꢂ 10ꢀ5 mol Lꢀ1 of the
ligands and the complexes in dichloromethane. 20 ꢁC.
The LUMO of Pt-1 is calculated as ꢀ2.56 eV, compared to the
LUMO energy level of ꢀ1.58 eV for ppyPt(acac) (Fig. 4). Both
complexes show similar HOMO energy levels, i.e. ꢀ5.63 eV and
ꢀ5.41 eV, respectively. These results indicate that NI fragment
serves as an electron-sink and the LUMO is significantly stabi-
lized (Fig. 4).
Pt-5 emits at 560 nm (Fig. 3d). The O2 sensitivity of Pt-5 is
lower than Pt-4 (Fig. 3c), due to the shorter s value of Pt-5 (0.86
ms) than Pt-4 (15.8 ms) (Table 1). The HOMO and LUMO energy
levels of Pt-5 are calculated as ꢀ5.63 eV and ꢀ2.18 eV,
The HOMO and LUMO energy level of Pt-2 is calculated as
ꢀ5.74 eV and ꢀ2.23 eV, respectively. Compared to Pt-1, the
9778 | J. Mater. Chem., 2010, 20, 9775–9786
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Fig. 3 Emission of the complexes in solution under a difference atmosphere of nitrogen, air and oxygen. (a) Pt-1, lex ¼ 390 nm. (b) Pt-2, lex ¼ 350 nm.
(c) Pt-4, lex ¼ 369 nm, (d) Pt-5, lex ¼ 400 nm. The solution is purged with N2 or O2 for about 20 min before measurement. 1.0 ꢂ 10ꢀ5 mol dmꢀ3 in
dichloromethane. 20 ꢁC. The asterisk (*) in b indicates the second order transition of the monochromator of the fluorescence spectrometer.
LUMO is less stabilized (Fig. 4). Thus we propose the p-conju-
gation is essential for the electron-sink effect of NI.
withdrawing fragments appended on the ppy ligand (e.g. Pt-1).
The location of the LUMO orbital of the complexes can be
changed by the substituents. For example, the LUMO is
predominantly distributed on NI moiety (Pt-1), not the pyri-
dine moiety for typical ppyPt(acac) complex. Furthermore, an
elevated HOMO and decreased LUMO were found for the
complex containing a p-conjugated ppy ligand (Pt-4), thus
a decreased HOMO–LUMO energy gap resulted. These find-
ings will be helpful for the design of new phosphorescent
cyclometalated Pt complexes.
The energy levels of HOMO and LUMO of Pt-4 were calcu-
lated as ꢀ5.22 eV and ꢀ1.90 eV, respectively (Fig. 4). For
ppyPt(acac), the HOMO/LUMO energy levels were calculated as
ꢀ5.41 eV and ꢀ1.58 eV, respectively. The p-conjugation desta-
bilizes the HOMO but stabilizes the LUMO, thus the HOMO–
LUMO energy gap is decreased.
We can clearly see that the LUMO orbital can be signifi-
cantly stabilized by the electron-sink effect of the electron-
Table 1 Photophysical parameters of the ligands and the platinum complexes
Emission propertiesa
abs/nma
3 ꢂ 10ꢀ4 /cmꢀ1 molꢀ1dm3
lem
F (%)
I0/I100
se
a
d
l
L-1
L-2
L-3
Pt-1
247/301/382 (399s)
229/321
235/334 (352s)
243/296/390
4.48/2.53/3.81(3.56)
2.07/5.58
5.34/4.77(3.98)
5.20/2.38/3.37
455
373
383
455/638
40.0%b
1.2
1.2
1.1
109.0
1.7 ns
0.8 ns
1.4 ns
455 nm: 3.2 ns
640 nm: 6.6 ms
386 nm: 25 ns
538 nm: 25.5 ms
5.4 ms
68.6%b
73.9%b
0.06%b/1.1%c
Pt-2
240/293/336/357/400
5.46/2.28/2.32/1.73/0.412
386/538
0.38%b/18.2%c
126.7
Pt-3
Pt-4
Pt-5
240/255/292/396
234/339 (352s)
253/297/321/335/400
3.17/3.23/2.76/0.51
3.81/2.51(2.39)
4.67/3.41/2.77/2.68/0.63
536
575
560
32.3%c
9.1%c
4.5%c
44.9
117.0
6.8
15.8 ms
0.86 ms
a
In deaerated DCM solution (1.0 ꢂ10ꢀ5 mol dmꢀ3). s stands for shoulder absorption peaks. b Result of deaerated solution, with quinine sulfate as the
c
standard (F ¼ 0.547 in 0.05 M sulfuric acid). Estimated error limit is 5%. Result of deaerated solution, with complex (Phen)Ru(bpy)2 (F ¼ 0.06 in
d
e
MeCN) as the standard. Estimated error limit is 5%. The emission intensity ratio of the complexes under N2 and O2 atmosphere. Luminescent
lifetimes.
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trap, the electronic structure of the excited state of the complex is
perturbed compared to ppyPt(acac).
To study the UV-vis absorption, the singlet excited states were
calculated (ESI†). The vertical excitation energy of S0 / S1
transition is 452 nm, which is in good agreement with the UV-vis
absorption (ca. 430 nm). The transition is 1IL (ppy/naph-
thalimide) and 1MLCT (Pt / ppy and Pt/naphthalimide) and
NI moiety contributes significantly to this transition.
The triplet excited states of Pt-1 were investigated (Table 2), to
study the emission. The calculated S0 / T1 energy difference is
666 nm, which is in good agreement with the experimental results
(lem ¼ 638 nm).12 The T1 state can be recognized with
a 3IL/3MLCT mixed feature, i.e. ppy / NI, Pt / ppy, Pt / NI
and acac / NI electron transfer, with the NI as the electron
acceptor. These results indicate that the NI group serves as an
electron-sink for the emissive excited state (T1), the LUMO is
localized on NI, not pyridine moiety.
Fig. 4 Energy levels of the frontier molecular orbitals (HOMO and
LUMO) of the complexes: effect of the electron-donating and electron-
withdrawing group. The HOMO and LUMO energy gaps are also
shown. Calculated by DFT at the B3LYP/6-31G(d)/LanL2DZ level using
Gaussian 09.
The geometry of Pt-2 is different from that of Pt-1 (Fig. 5).
The NI group takes an orthogonal orientation toward the ppy
coordination plan. The LUMO is localized on the ppy fragment,
not the NI group. This means that without p-conjugation, the
electron-sink effect of the NI group in Pt-2 is much weaker than
that in Pt-1. For Pt-2, the HOMO is mainly distributed on the Pt,
the acac ligand and the phenyl group of the ppy ligand.
The photophysical properties of the ligands and the complexes
were summarized in Table 1. The luminescent lifetime of Pt-1 is
longer than that of Pt-3 (Table 1). This is probably due to the
3
more significant IL component of the emissive state of Pt-1.23
which is supported by the TDDFT calculations. We noticed
a cyclometalated Pt complex with electron-deficient fluoren-9-
one attached to the ppy ligand shows two emission band, both
were assigned as 3MLCT emission.5d In the case of Pt-1 and Pt-2,
however, fluorescence/phosphorescence dual emission was
observed and the separation of the fluorescence/phosphorescence
emission band (by 200 nm) is more significant, which is beneficial
for luminescent ratiometric O2 sensing.6,7
TDDFT indicates the S0 / S1 transition energy of Pt-2 is 423
nm (ESI†), which is close to the experimental result (400 nm).
Furthermore, the small oscillator strength (f) (0.0498) of S1 state
indicates that the absorption is much weaker than that of Pt-1
(S1 state of Pt-1 has a much higher f value of 0.4456, ESI†). This
theoretical prediction is proved by the UV-vis absorptions
(Fig. 2). The energy gap of S0 – T1 of Pt-2 is calculated as 541 nm
(Table 2), which is close to the experimental results (lem
¼
3
538 nm, Fig. 3).12 The main transitions of the T1 state are IL
We investigated the UV-vis absorption as well as the photo-
luminescence emission spectra of the complexes at different
concentrations and no self-quenching was observed. All the
results infer that there is no significant PtII/PtII interaction for
these complexes in solution (see ESI†).45–47
3
3
(NI localized), LLCT (NI / ppy), MLCT (Pt / NI) and
3
3LLCT (ppy / NI). The significant IL component of the T1
state of Pt-2 infers that the luminescent lifetime will be
3
3
extended.24 An equilibrium between the MLCT and IL states
probably exists. This prediction was verified by the s value of
Pt-2 (25.5 ms), which is longer than Pt-1 (6.6 ms) (Table 1).
No 3IL character was found for the T1 state of Pt-3 (see ESI†).
Thus, we expect a relatively short luminescent lifetime and higher
luminescent quantum yield for Pt-3.8,24 These expectations were
supported by the experimental results (Table 1). The luminescent
lifetime of Pt-3 is determined as 5.4 ms, vs. 25.5 ms for Pt-2.
For Pt-4, the pyridine fragment of the ppy ligand serves as the
electron acceptor, which is different from Pt-1. The T1 state of
Pt-4 can be assigned as a 3IL transition (naphthal/pyridine).
The rationalization of the photophysical properties of the
complexes demonstrate the potential of DFT/TDDFT calcula-
tions for the rational design of luminescent transition metal
complexes with predetermined photophysical properties.
Rationalize the photophysical properties of the ppyPt(acac)
complexes with DFT/TDDFT calculation: assignment of the
UV-vis absorption and the emissive triplet excited states
Recently, density functional theory (DFT) and time-dependent
DFT (TD-DFT) were used in the study of photophysical prop-
erties of the luminophores.24a–d,34,48–57 Herein we performed DFT
calculations to study the photophysical properties of the
complexes.
A distorted planar square Pt coordination center was found
ꢀ
for Pt-1, with a Pt–O bond length in the range 2.037–2.141 A
ꢀ
(Fig. 5). Pt–N and Pt–C bond lengths are calculated as 2.024 A
ꢀ
and 1.985 A, respectively, which are in good agreement with the
single crystal structures (Fig. 1). The NI moiety takes a coplanar
geometry with the ppy plan, which is consistent with the single
crystal structure of Pt-1 (Fig. 1).
Oxygen sensing in polymer films: quantification of the sensitivity
towards O2
The HOMO of Pt-1 is localized on the phenyl group of ppy, the
NI group and the Pt atom (Fig. 5). Interestingly, LUMO is
distributed on NI, which is different from ppyPt(acac), for which
the LUMO is predominantly localized on the pyridine group of
ppy.4,5d,8 These results infer that the NI group acts as electron
Much attention has been paid to luminescent oxygen sensing.58–65
However, very few cyclometalated Pt(II) or Ir(III) complexes
have been used for luminescent oxygen sensing. Previously
a cyclometalated Ir(III) complex as a luminscent O2 sensing
9780 | J. Mater. Chem., 2010, 20, 9775–9786
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Fig. 5 Frontier molecular orbitals of (a) Pt-1 and (b) Pt-2. H stands for HOMO and L stands for LUMO. Calculated by DFT at the B3LYP/6-31G(d)/
LanL2DZ level using Gaussian 09.
material was reported.25 Herein we studied the luminescent O2
sensing properties of the new complexes, which have longer
luminescent lifetimes than the recently reported oxygen sensing
cyclometalated Ir(III) complex (s ¼ 4.3 ms).23 Furthermore, the
emission wavelength of the complexes is longer than the reported
Ir complex for O2 sensing.25
a significant quenching effect and fast response.23,24,66 The
response time (tY95) and recovery time (t[95) are usually used for
the evaluation of the response of O2 sensing films,23,24 which are
generally accepted as the time for the luminescence intensity
changes to reach 95% of the overall variation, when the gas was
switched between different O2 partial pressures, such as from
100% N2 to 100% O2, or vice versa.
For practical O2 sensors, phosphorescent dyes are usually
embedded in solid matrixes, such as polymer films.6,7,23,24 We
demonstrated that a IMPEK-C polymer (the structures are
shown in Scheme 1) is an ideal matrix for O2 sensing, and offers
We found that the tY95 and the t[95 for Pt-1 is 4 s and 6 s,
respectively (Fig. 6a). Short response and recovery times are
usually found for O2 sensors with porous supporting materials,
Table 2 Electronic excitation energies (eV), main configurations and CI coefficients of the low-lying triplet electronically excited states of complexes Pt-
1 and Pt-2, calculated by TDDFT//B3LYP/6-31G(d)/LanL2DZ, based on the DFT//B3LYP/6-31G(d)/LanL2DZ Optimized Ground State Geometries
TDDFT//B3LYP/6-31G(d)
Electronic transition
Energya
fb
Compositionc
CId
Character
Pt-1
S0 / T1
1.86 eV 666 nm
0.0000e
H ꢀ 4 / L (15%)
H ꢀ 4 / L + 1 (15%)
H ꢀ 2 / L (21%)
H ꢀ 1 / L (34%)
H/ L (63%)
H ꢀ 2 / L + 1 (71%)
H ꢀ 2 / L (21%)
H ꢀ 1 / L + 1 (16%)
H ꢀ 3 / L + 1 (16%)
0.1478
0.1493
0.2110
0.3419
0.6331
0.7118
0.2058
0.1585
0.1530
ILCT
ILCT
MLCT, LLCT, ILCT
MLCT, LLCT, ILCT
MLCT, ILCT
MLCT
LLCT, MLCT
ILCT, LLCT
MLCT
Pt-2
S0 / T1
2.29 eV 541 nm
0.0000e
a
Only the selected low-lying excited states are presented. b Oscillator strength. c H stands for HOMO and L stands for LUMO. The relative percentage
contributions (absolute values) are listed in parentheses (derived from the.log files with software GaussSum 2.1). Only the main configurations are
presented. d The CI coefficients are in absolute values. e No spin-orbital coupling effect was considered, thus the f values are zero.
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Fig. 6 Phosphorescent emission intensity response of the complexes to step variations of O2 concentration levels (a) emission change of Pt-1 film vs.
O2/N2 saturation switch, lex ¼ 430 nm, lem ¼ 640 nm. (b) Dynamic response of the Pt-1 film vs. small steps of variation of O2 partial pressure, lex
¼
430 nm, lem ¼ 640 nm. (c) Dynamic response of the Pt-2 film vs. small steps of variation of O2 partial pressure, lex ¼ 400 nm, lem ¼ 529 nm. (d) Fitting of
the oxygen sensing property of the IMPEK-C films of complexes based on the two site model (eqn (1)).
such as MCM-41 or organically modified gel (ormosils).5,67–70
Our strategy for the film preparation (dissolving and casting) is
straight forward and it is ideal for practical O2 sensing applica-
tions. Furthermore, the emission of the Pt-1 film was quenched
by increasing the O2 partial pressure (Fig. 6b).
(f1 + f2 ¼ 1). Each portion has a different accessibility to O2, thus
the two portions show different quenching constants (KSV1 and
KSV2, eqn (1)).
I0
I
1
¼
(1)
f1
f2
þ
The sensitivity of Pt-2 toward O2 is much higher than that of
Pt-1 (Fig. 6c). For example, the emission of Pt-2 sensing film is
significantly quenched under 3.5% O2.
1 þ KSV1pO
1 þ KSV2pO
2
2
In order to quantitatively compare the O2 sensing property of
the complexes, the O2 sensing data was fitted with the two-site
model (Fig. 6d) and the fitting results are summarized in Table 3.
The sensitivity of Pt-3 towards O2 is lower than Pt-1, with 3.5%
O2, the emission of Pt-3 was quenched by ca. 19.5% (see ESI†).
The recovery time of Pt-3 is short (5.3 s). The O2 sensing property
of Pt-4 and Pt-5 were also studied, fast response and recovery time
were observed (see ESI†). Pt-4 is more significantly quenched
compared to Pt-5, which is in agreement with the longer lumi-
nescent lifetime of Pt-4 (s ¼ 15.8 ms) than Pt-5 (s ¼ 0.86 ms).
It should be pointed out the photo-stability of the complexes is
excellent, i.e. the emission response of the sensing films is fully
reversible, even with long periods of continuous irradiation with
UV light (Fig. 6). No decomposition of the films was observed.
Previously we found that the O2 sensing films of PtOEP show
slightly decreased emission intensity after long periods of
continuous irradiation, possibly due to the decomposition of the
PtOEP complexes.23
Complex Pt-2 is the best one for O2 sensing among the complexes
app
studied herein, i.e. with the highest quenching constant (KSV
0.234 Torrꢀ1, or 0.31 mbarꢀ1), which is 117-fold of Pt-5. The
¼
order of the sensitivity of the complexes (the magnitude of the
app
KSV values) are in line with the order of the luminescent life-
times of the complexes (Table 1). Furthermore, the O2 sensitivity
of the new complexes is generally high, in particular Pt-2 is
66-fold higher than the previously reported cyclometalated
Ir(III) complex for O2 sensing purpose (s ¼ 4.3 ms and quenching
constant Ksv ¼ 4.7 ꢂ 10ꢀ3 mbarꢀ1), which is prepared with ppy
ligands capped with diphenylamine moieties.25
Conclusions
For heterogeneous O2 sensing films, a modified Stern–Volmer
or two-site model is required for fitting the quenching data.23,69 In
the two-site model, the O2-sensitive dyes are considered as two
different portions, which are defined as f1 and f2, respectively
Inconclusion, we have synthesized a seriesof novel cyclometalated
Pt(II) (acac) complexes based on aryl-ethynylated ppy ligands. To
our knowledge, this is the first time that aryl ethynylenes (C^C)
9782 | J. Mater. Chem., 2010, 20, 9775–9786
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were used to extend the p-conjugation of the ppy ligand to perturb
the electronic structures of the emissive excited states, and thus to
tune the photophysical properties, such as the emission color and
the luminescent lifetimes of the cyclometalated Pt(II) complexes.
All the complexes show room temperature phosphorescence in
fluid solution. The complex with ethynylated naphthalimide (NI)
on the ppy ligand (Pt-1) shows unexpected red-shifted emission in
the deep red/near IR range (638–800 nm), which is red-shifted by
(6 mL) and triethylamine (2 mL) were mixed together. Then
Pd(PPh3)2Cl2 (0.042 mmol, 29.3 mg, 5 mol%), PPh3 (0.042 mmol,
10.2 mg, 5 mol%) and CuI (8.0 mg, 0.042 mmol, 5 mol %) were
added. The reaction mixture was heated at 60 ꢁC and stirred
under argon for 6 h. After completion of the reaction, the
mixture was cooled to room temperature and the yellow
precipitate was collected by filtration, and the crude product was
purified with column chromatography (silica gel, CH2Cl2 as the
elute) to give 300.0 mg yellow solid (83.3%). 1H NMR (400 MHz,
CDCl3): 8.76 (d, 2H, J ¼ 8.3 Hz), 8.65 (d, 1H, J ¼ 7.2 Hz),
8.57 (d, 1H, J ¼ 7.8 Hz), 8.11 (d, 2H, J ¼ 8.3 Hz), 7.98 (d, 1H, J ¼
7.5 Hz), 7.85 (t, 1H, J ¼ 7.8 Hz), 7.79 (d, 4H, J ¼ 8.5 Hz),
7.31–7.28 (m, 1H), 4.19 (t, 2H, J ¼ 7.5 Hz), 1.77–1.69 (m, 2H),
1.51–1.42 (m, 2H), 0.99 (t, 3H, J ¼ 7.3 Hz). 13C NMR (100 MHz,
CDCl3):d 164.01, 163.75, 156.25, 149.90, 136.91, 132.35, 131.60,
130.82, 130.36, 128.10, 127.48, 127.01, 123.07, 122.75, 122.26,
up to 150 nm compared to the parent complex ppyPt(acac) (lem
¼
486 nm). Interestingly, complex Pt-2, with disrupted p-conjuga-
tion between the NI and the ppy subunits, shows emission at much
shorter wavelength (lem ¼ 538 nm). The drastically red-shifted
emission of Pt-1 was rationalized by the DFT/TDDFT calcula-
tions, which indicates a significant electron-sink effect of the NI
moiety in Pt-1, but not in Pt-2. The luminescent lifetimes of the
complexes were tuned from 0.86 ms to 25.5 ms, correspondingly the
luminescent O2 sensing can be improved by 117-fold (Stern–
120.68,
98.92,
87.50,
40.34,
30.23,
20.40,
13.85.
Volmer quenching constantsKSV ¼ 0.234 Torrꢀ1 for Pt-2vs. KSV
¼
ESI-HRMS ([C29H22N2O2 + H]+): calcd, m/z ¼ 431.1760, found,
0.002 Torrꢀ1 for Pt-5). Our emission color tuning strategy by using
electron-sink or C^C bridged p-conjugated ligand to perturb the
electronic structure of the excited states of the complexes, exten-
sion of the p-conjugation of the ppy ligand via aryl-ethynylene
moieties, and the assignment of the electronic structures of the
emissive excited states of the complexes with DFT/TDDFT
calculations will be useful for design and application of novel
luminescent transition metal complexes.
m/z ¼ 431.1769.
Pt-1 and Pt-2
Compound L-1 (260 mg, 0.6044 mmol) was dissolved in mixed
solvent of 2-ethoxyethanol (6 mL) and water (2 mL), then
K2PtCl4 (125.4 mg, 0.302 mmol) was added, the mixture was
heated at 80 ꢁC for 16 h under argon atmosphere. After cooling
to room temperature, the mixture was poured into water (20 mL)
and the precipitate was collected and washed with water (4 ꢂ
20 mL). The precipitate was reacted with Hacac (90.7 mg,
0.907 mmol) in the presence of Na2CO3 (320 mg, 3.02 mmol) in
Table 3 Parameters of O2 sensing film with IMPEK-C as supporting
matrix (fitting result of the data in Fig. 6 with the two site model, eqn (1))
KSV app d KSV app e pO2/Torrf
a
a
f2
b
b
KSV1 KSV2 r2
c
ꢁ
f1
2-ethoxyethanol (6 mL) at 100 C for 16 h under argon atmo-
sphere. The mixture was poured into water, the precipitate was
purified with column chromatography (silica gel, CH2Cl2 as
eluent), the first band was collected to afford the product Pt-1 as
a yellow solid in 10.0% yield (22.0 mg). After the compound Pt-1
was collected, the eluent was changed to DCM/MeOH (100 : 1,
v/v), and a yellow band of Pt-2 was collected. A yellow solid was
obtained, yield: 10.9% (25.0 mg).
Pt-1 0.265 0.735 0.062 0.000 0.9998 0.016
Pt-2 0.382 0.618 0.613 0.000 0.9954 0.234
Pt-3 0.321 0.680 0.008 0.000 0.9993 0.003
Pt-4 0.596 0.404 0.037 0.000 0.9990 0.022
Pt-5 0.242 0.758 0.008 0.000 0.9997 0.002
0.021
0.312
0.004
0.029
0.003
62.5
4.3
333.0
45.5
500.0
a
b
The respective ratio of the two portion of the dyes. The quenching
c
constants of the two portions. The determination coefficients.
d
app
Weighted quenching constant, KSV
.
¼ f1 ꢂ KSV1 + f2 ꢂ KSV2. In
e
f
Torrꢀ1
pressure at which the initial emission intensity of film is quenched by
In mbarꢀ1. 1 Torr ¼ 1.3332 mbar. The oxygen partial
Pt-1
50%, and can be calculated as 1/KSV. In Torr.
1H NMR (400 MHz, CDCl3): 9.04 (d, 1H, J ¼ 5.8 Hz), 8.81 (d,
1H, J ¼ 8.5 Hz), 8.63 (d, 1H, J ¼ 7.3 Hz), 8.56 (d, 1H, J ¼
7.8 Hz), 7.97 (d, 1H, J ¼ 7.6 Hz), 7.87–7.80 (m, 3H), 7.66 (d, 1H,
J ¼ 8.1 Hz), 7.48 (d, 1H, J ¼ 8.0 Hz), 7.42 (d, 1H, J ¼ 7.8 Hz),
7.18 (t, 1H, J ¼ 6.5 Hz), 5.51 (s, 1H), 2.08 (s, 3H), 2.04 (s, 3H),
4.19 (t, 2H, J ¼ 7.5Hz), 1.77–1.68 (m, 2H), 1.51–1.42 (m, 2H),
0.99 (t, 3H, J ¼ 7.6 Hz). 13C NMR (100 MHz, CDCl3):d 185.95,
184.26, 167.22, 164.10, 163.83, 147.49, 145.83, 138.59, 138.27,
133.49, 132.61, 131.76, 131.48, 130.64, 130.38, 128.13, 128.05,
127.26, 122.98, 122.63, 122.35, 121.94, 121.84, 118.93, 102.65,
100.59, 87.29, 40.43, 30.25, 29.58, 28.23, 27.21, 20.41, 13.85.
MALDI-MS: ([C34H28N2O4Pt]+) calcd, m/z ¼ 723.1697, found,
m/z ¼ 723.1633.
Experimental
General information
NMR spectra were recorded on a 400 MHz Varian Unity Inova
NMR spectrophotometer. Mass spectra were recorded with
Q-TOF Micro MS spectrometer. UV-vis absorption spectra were
measured with a HP8453 UV-visible spectrophotometer. Fluo-
rescence spectra were recorded on JASCO FP-6500 or a Sanco
970 CRT spectrofluorometer. Phosphorescence quantum yields
were measured with reference (Phen)Ru(bpy)2 (F ¼ 0.06 in
MeCN). Luminescent lifetimes were measured on a Horiba Jobin
Yvon Fluoro Max-4 (TCSPC) instrument.
Pt-2
L-1
1H NMR (400 MHz, CDCl3):9.04 (d, 1H, J ¼ 5.8 Hz),
8.62 (d, 1H, J ¼ 7.3 Hz), 8.58 (d, 1H, J ¼ 7.6 Hz), 8.37 (s, 1H),
8.27 (d, 1H, J ¼ 8.5 Hz), 7.90 (t, 1H, J ¼ 7.8 Hz), 7.80 (d, 1H,
Under Ar, 4-bromo-1,8-naphthalimide (276.4 mg, 0.837 mmol),
2-(4-ethynylphenyl)pyridine (150 mg, 0.837 mmol), dry ethanol
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J ¼ 8.0 Hz), 7.75–7.69 (m, 3H), 7.57 (d, 1H, J ¼ 8.2 Hz), 7.26–
7.23 (m, 1H), 5.52 (s, 1H), 4.96 (s, 2H), 4.19 (t, 2H, J ¼ 7.5 Hz),
2.05 (s, 3H), 2.02 (s, 3H), 1.76–1.68 (m, 2H), 1.50–1.41 (m, 2H),
0.98 (t, 3H, J ¼ 7.2 Hz). 13C NMR (100 MHz, CDCl3):d 196.86,
186.24, 184.18, 164.31, 164.13, 147.74, 139.63, 138.56, 135.67,
131.01, 130.95, 130.69, 130.29, 129.30, 128.59, 126.99, 123.91,
123.24, 123.03, 122.68, 122.06, 119.54, 102.76, 43.65, 40.22,
30.22, 28.26, 27.21, 20.39, 13.87. MALDI-MS: (C34H30N2O5Pt)
calcd, m/z ¼ 741.1803, found, m/z ¼ 741.1853.
L-3
Under
argon
atmosphere,
2-(40-bromophenyl)pyridine
(459.6 mg, 1.97 mmol), 1-ethynylnaphthalene (6) (300.0 mg,
1.97 mmol), a mixed deaerated solvent of toluene (10 mL) and
(i-Pr)2NH (10 mL) was mixed together. Then Pd(PPh3)4
(71.9 mg, 0.06 mmol), CuI (24.6 mg, 0.12 mmol) were added.
Then the mixture was refluxed for about 8 h. The reaction
mixture was cooled to r.t. and the solvent was removed under
reduced pressure. Water was added and the mixture was
extracted with dichloromethane. The combined organic layer
was dried over anhydrous Na2SO4. After removal of the solvent
the crude product was purified with column chromatography
(silica gel, DCM:hexane ¼ 1 : 1, v/v) A pale solid was obtained,
200.0 mg, yield 33.3%. 1H NMR (400 MHz, CDCl3): 8.73 (d, 1H,
J ¼ 4.8 Hz), 8.48 (d, 1H, J ¼ 8.3 Hz), 8.07 (d, 2H, J ¼ 8.1 Hz),
7.86 (t, 2H, J ¼ 8.0 Hz), 7.80–7.75(m, 5H), 7.62 (t, 1H, J ¼
7.0 Hz), 7.54 (t, 1H, J ¼ 7.6 Hz), 7.47 (t, 1H, J ¼ 7.8 Hz),
7.27–7.24 (m, 1H). 13C NMR (100 MHz, CDCl3): d 156.42,
149.61, 138.86, 137.05, 133.23, 132.08, 130.49, 128.91, 128.34,
126.89, 126.48, 126.21, 125.30, 124.10, 122.44, 120.79, 120.67,
94.19, 88.92. ESI-HRMS: calcd ([C23H15N + H]+), m/z ¼
306.1283, found, m/z ¼ 306.1289.
L-2
Under argon atmosphere, 2-(40-bromophenyl) pyridine
(386.9 mg, 1.655 mmol), 4-ethynylbenzonitrile (5) (210 mg, 1.66
mmol), a mixed deoxygenated solvent of dry ethanol (6 mL) and
triethylamine (2 mL) was mixed together. Then Pd(PPh3)2Cl2
(57.9 mg, 0.093 mmol, 5 mol %), PPh3 (19.7 mg, 0.093 mmol,
5 mol%) and CuI (15.7 mg, 0.093 mmol, 5 mol%) was added. The
reaction mixture was heated at 60 ꢁC and stirred under argon for
6 h. After completion of the reaction, the mixture was cooled to
room temperature. The solvent was removed under reduced
pressure, water was added and the mixture was extracted with
CH2Cl2 (4 ꢂ 20 mL). The combined organic layer was dried over
anhydrous Na2SO4. After removal the solvent, the crude product
was purified with column chromatography (silica gel,
CH2Cl2:petroleum ether ¼ 2 : 1, v/v), light yellow solid was
abstained (210.0 mg, 45.3%). 1H NMR (400 MHz, CDCl3)
8.74 (d, 1H, J ¼ 3.5 Hz), 8.06 (d, 2H, J ¼ 8.1 Hz), 7.83–7.77
(m, 2H) 7.67–7.61 (m, 6H) 7.29 (t, 1H, J ¼ 5.5 Hz). 13C NMR
(100 MHz, CDCl3): d 156.08, 149.53, 139.43, 137.27, 132.26,
132.10, 128.12, 126.99, 122.92, 122.69, 120.83, 118.52, 111.58,
99.99, 93.61, 89.02. ESI-HRMS: ([C20H12N2 + H]+) calcd, m/z ¼
281.1079, found, m/z ¼ 281.1083.
Pt-4 and Pt-5
L-3 (110.0 mg, 0.36 mmol) was dissolved in mixed solvent of
2-ethoxyethanol (6 mL) and water (2 mL), then K2PtCl4
(74.8 mg, 0.18 mmol) was added, the mixture was heated at 80 ꢁC
for 16 h under argon atmosphere. After cooling to room
temperature, the mixture was poured into water (20 mL) and the
precipitate was washed with water (4 ꢂ 20 mL) and dried under
vacuum. The precipitate was treated with Hacac (54.0 mg,
0.54 mmol), in the presence of Na2CO3 (190.8 mg, 1.80 mmol), in
2-ethoxyethanol (6 mL) as solvent at 100 ꢁC for 16 h under argon
atmosphere. The mixture was poured into water, the precipitate
was purified with column chromatography (silica gel, CH2Cl2 as
the eluent). The first band was collected to afford the product
Pt-4 as a yellow solid in 13.9% yield (15.0 mg, 0.025 mmol), and
the second band was collected to afford the product Pt-5 as
a yellow solid, 25.0 mg. Yield: 22.0%.
Pt-3
L-2 (130.0 mg, 0.464 mmol) was dissolved in mixed solvent of
2-ethoxyethanol (6 mL) and water (2 mL), then K2PtCl4
(96ꢁ.3 mg, 0.232 mmol) was added, the mixture was heated at
80 C for 16 h under argon atmosphere. After cooling to room
temperature, it was added to water (20 mL) and the precipitate
was washed with water (4 ꢂ 20 mL) and dried under vacuum.
The precipitate was then treated with Hacac (69.6 mg,
0.696 mmol), in the presence of Na2CO3 (245.9 mg, 2.32 mmol),
in 2-ethoxyethanol (6 mL) at 100 ꢁC for 16 h under argon
atmosphere. The mixture was then poured into water, the
precipitate was purified with column chromatography (silica gel,
CH2Cl2 as an eluent) to afford the product as a yellow solid in
22.8% yield (32.0 mg). 1H NMR (400 MHz, CDCl3) 9.06 (d, 1H,
J ¼ 5.7 Hz), 8.22 (s, 1H), 7.87 (t, 1H, J ¼ 7.8 Hz), 7.73–7.71
(m, 2H), 7.63 (d, 2H, J ¼ 8.1 Hz), 7.52 (d, 1H, J ¼ 8.2 Hz), 7.43
(d, 2H, J ¼ 8.1 Hz), 7.22 (t, 1H, J ¼ 6.8 Hz), 5.52 (s, 1H), 4.42
(s, 2H), 2.05 (s, 3H), 2.03 (s, 3H). 13C NMR (100 MHz, CDCl3):
d 197.04, 186.25, 184.10, 166.69, 149.76, 147.71, 140.62, 139.11,
135.75, 132.28, 130.58, 130.42, 123.84, 122.94, 122.60, 119.48,
118.89, 110.76, 102.71, 45.56, 28.24, 27.20. MALDI-MS:
1
Pt-4. H NMR (400 MHz, CDCl3): 9.02 (d, 1H, J ¼ 5.7 Hz),
8.53 (d, 1H, J ¼ 8.4 Hz), 7.87–7.78 (m, 5H), 7.63–7.58 (m, 2H),
7.53 (t, 1H, J ¼ 7.7 Hz), 7.46 (t, 2H, J ¼ 8.0 Hz), 7.40 (d, 1H, J ¼
8.1Hz), 7.13 (t, 1H, J ¼ 6.6 Hz), 5.50 (s, 1H), 2.07 (s, 3H),
2.02 (s, 3H). 13C NMR (100 MHz, CDCl3): d 185.94, 184.47,
167.60, 147.54, 145.02, 138.47, 138.36, 133.51, 133.37, 130.48,
128.77, 128.42, 127.19, 126.84, 126.62, 126.54, 125.48, 123.77,
122.81, 121.67, 121.42, 118.93, 102.80, 95.82, 88.68, 29.89, 28.44,
27.40. MALDI-MS: calcd ([C28H21NO2Pt + H]+), m/z ¼
599.1298, found, m/z ¼ 599.1258.
1
Pt-5. H NMR (400 MHz, CDCl3): 9.38 (d, 1H, J ¼ 8.7 Hz),
9.06 (d, 1H, J ¼ 5.5 Hz), 8.21 (d, 1H, J ¼ 1.5 Hz), 8.11 (d, 1H,
J ¼ 8.3 Hz), 8.01 (d, 1H, J ¼ 7.2 Hz), 7.94 (d, 1H, J ¼ 8.0 Hz),
7.88 (t, 1H, J ¼ 8.1 Hz), 7.76 (t, 1H, J ¼ 8.0 Hz), 7.71 (t, 2H, J ¼
8.3 Hz), 7.61 (t, 1H, J ¼ 7.5 Hz), 7.55 (d, 1H, J ¼ 8.0 Hz), 7.49
(t, 1H, J ¼ 7.8 Hz), 7.23 (t, 1H, J ¼ 7.0 Hz), 5.41 (s, 1H), 1.99
([C25H20N2O3Pt
+
H]ꢀ) calcd, m/z
¼
592.1205, found,
m/z ¼ 592.1495.
9784 | J. Mater. Chem., 2010, 20, 9775–9786
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(s, 3H), 1.74 (s, 3H). 13C NMR (100 MHz, CDCl3): d 198.33,
195.93, 186.04, 184.69, 166.71, 151.34, 147.97, 139.74, 138.59,
135.15, 134.30, 132.89, 132.16, 131.08, 129.40, 129.05, 128.86,
127.09, 126.34, 125.45, 124.74, 123.07, 122.97, 119.86, 102.69,
29.88, 28.32, 26.95. MALDI-MS: calcd ([C28H21NO4Pt]ꢀ), m/z ¼
630.1118, found, m/z ¼ 630.1169.
Dalian University of Technology (SFDUT07005 and
1000-893394) for financial support.
References
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X-Ray structural analysis
Single-crystal X-ray diffraction data were obtained on a Bruker
SMART APEX CCD diffractometer using a graphite mono-
ꢀ
chromated MoKa (l ¼ 0.71073 A) using the SMART and
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data reduction using Shelxtl 97 software the absorption effect
was corrected for as well. Crystallographic data for the structures
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Crystallographic Data Centre as supplementary publication
material. The CCDC number for Pt-1 and Pt-5 are 762732, and
762731, respectively. Copies of this information can be obtained
free of charge from The Director, CCDC, 12 Union Road,
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Oxygen sensing films
Typical film preparation is as following. 10.0 mg of IMPEK-C
polymer was dissolved in 0.5 mL chloroform, then 0.4 mL of
cyclometalated platinum complexes solution in DCM (1.0 ꢂ 10ꢀ3
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DFT calculations
The structures of the complexes were optimized using density
functional theory (DFT) with B3LYP functional and 6-31G(d)/
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Acknowledgements
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We thank the NSFC (20642003, 20634040 and 20972024),
Ministry of Education (SRFDP-200801410004 and NCET-08-
0077), NKBRSF (2007CB815202), the Royal Society (UK) and
the NSFC (China) (China-UK Cost-Share Science Networks
21011130154), State Key Laboratory of Fine Chemicals
(KF0710 and KF0802), State Key Laboratory of Chemo/Bio-
sensing and Chemometrics (2008009), the Education Depart-
ment of Liaoning Province (2009T015), PCSIRT (IRT0711) and
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