Tuning the emission property of carbazole-caped cyclometalated platinum(II) complexes and its application for enhanced luminescent oxygen sensing

Article abstract of DOI:10.1016/j.jorganchem.2011.03.002

Carbazole-caped cyclometalated platinum(II) complexes aryl-R-ppyPt(acac) (where ppy = 4-phenylpyridine, acac = acetylacetonato, aryl = carbazole and R is linker) were synthesized. The carbazole group is attached to the ppy ligand via α-diketo moiety (Pt-1

Full text of DOI:10.1016/j.jorganchem.2011.03.002

Journal of Organometallic Chemistry 696 (2011) 2388e2398
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Tuning the emission property of carbazole-caped cyclometalated platinum(II)
complexes and its application for enhanced luminescent oxygen sensing
*
Wanhua Wu, Wenting Wu, Shaomin Ji, Huimin Guo, Jianzhang Zhao
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, 2 LingGong Road, Dalian 116024, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Carbazole-caped cyclometalated platinum(II) complexes aryl-R-ppyPt(acac) (where ppy ¼ 4-phenyl-
pyridine, acac ¼ acetylacetonato, aryl ¼ carbazole and R is linker) were synthesized. The carbazole group
Received 9 November 2010
Received in revised form
28 February 2011
is attached to the ppy ligand via
a
-diketo moiety (Pt-1) and (Pt-2) or CꢀC single bond (Pt-3), by
Sonogashira or Negishi coupling reactions. We found that the ethynylene bonds of the C^N ligands were
oxidized to -diketo or methylene-keto structure during the metalation with K2PtCl4. Emissions beyond
550 nm were observed for Pt-1, with electron-withdrawing -diketo moiety attached to ppy ligand,
compared to the emission at 486 nm for the parent complex ppyPt(acac). Extended phosphorescence
lifetime (sP ¼ 12.4 s) and enhanced phosphorescence quantum yield (FP ¼ 66%) were observed for Pt-3
compared to ppyPt(acac) (sP ¼ 2.4 s and FP ¼ 15%), we attribute the enhanced phosphorescence
property to the electron-donating carbazole substituent. With density functional theoretical calculations
(DFT), we found that the carbazole moiety is involved in the HOMO (Pt-3), the -diketo moiety is
Accepted 1 March 2011
a
a
Keywords:
Cyclometalated complex
Platinum
Oxygen sensing
Phosphorescence
Triplet state
m
m
a
Carbazole
involved in the LUMO (Pt-1), thus the energy gaps between the HOMO and LUMO in both cases were
decreased and red-shifted emission is expected, compared to ppyPt(acac). The different emission
properties of 1,2-dione containing complexes (Pt-1 and Pt-2) and the Pt-3 were rationalized by the spin
density surface analysis of the complexes. The luminescent O2 sensing properties of these complexes
were studied in solution and in polymer films, for which fast response time (3.3 s) and recovery time
(3.7 s) were observed. Two-site model fitting indicated that complex Pt-3 is the most sensitive O2
sensing material among the complexes studied herein, with quenching constant of KSV ¼ 0.0238 Torrꢀ1
.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
On the other hand, luminescent oxygen sensing is attracting
much attention due to its applications in biological, environmental,
chemical and clinical science [1,2]. Proper selection of phospho-
rescent dye is pivotal for luminescent O2 sensing. Currently, the
dyes for O2 sensing include polypyridine Ru(II) complexes, Pt(II)/Pd
(II) porphyrin complexes and more recently the cyclometalated
complexes [1,2]. We noticed that the ppyPt(acac) complexes show
Recently cyclometalated Pt(II) complexes, such as ppyPt(acac)
(ppy ¼ 2-phenylpyridine, acac ¼ acetylacetonato), attracted much
attention due to their applications in organic light emitting diodes
(OLED) [1ꢀ4], luminescent molecular sensors [5e7] and for their
photophysical properties [8e10]. These complexes show strong
triplet emission in fluid solution at room temperature, due to the
spin-orbit coupling effect of the heavy atom, which leads to the
population of 3MLCT/3IL emissive excited states of the complexes
upon photoexcitation. Typical cyclometalated Pt(II) complexes give
relatively short emission wavelength, e.g. at ca. 500 nm. Thus,
tuning the emission color is critical for electroluminescent mate-
rials. However, it is still a challenge to tune the emission color of the
phosphorescent lifetime in the range of microseconds (ms), which
are ideal for oxygen sensing [2]. To the best of our knowledge,
however, no systematic study has been carried out on the lumi-
nescent O2 sensing properties of the cyclometalated Pt(II)
complexes [11ꢀ19].
Recently we have been interested in synthesis of phosphorescent
metal complexes and studying the photophysical properties and
exploring their applications, such as in luminescent oxygen sensing
[20ꢀ25]. We and others found that the luminescent lifetimes of the
Ru(II) bispyridine complexes can be significantly tuned by ligand
modification (introduce of new triplet excited states) [20ꢀ28]. We
anticipate that the emission wavelength and phosphorescence life-
time of the cyclometalated Pt(II)(acac) complexes may probably be
Pt(II) complexes and we noticed that the p-conjugation framework
of the typical ppy ligands has never been extended by ethynylene
groups, to tune the emission wavelength of the complexes.
* Corresponding author. Tel./fax: þ86 (0)411 8498 6236.
E-mail address: zhaojzh@dlut.edu.cn (J. Zhao).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.03.002

W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
2389
tuned by the similar approach of ligand modification, thus we set
out to prepare new cyclometalated Pt(II) complexes to modulate the
photophysical properties and to explore the application of these
complexes for luminescent O2 sensing.
strengthen the ligand field of the ppy moiety, thus improve lumi-
nescence properties, such as prolonged phosphorescence lifetime
and higher phosphorescence quantum yields could be expected [3].
Furthermore, the electron-donating appendents on the phenyl
subunit of the ppy ligand may rise the energy level of the highest
occupied molecular orbitals (HOMO) of the cyclometalated Pt
complex, but the energy level of the lowest unoccupied molecular
orbital (LUMO) is unaffected, as a result the decreased HOMO-
LUMO energy gap leads to red-shifted emission, compared to the
The design rationales for the complexes are to extend the
p-conjugation framework of the ppy ligands by ethynylene groups
(eC^Ce). Carbozale was selected to attach to the phenyl moiety of
the ppy ligand to shift the emission wavelength to the red end of the
spectrum [3]. Thus we prepared new cyclometalated Pt complexes
with carbazole substituted ppy ligand and ethynylene group was
used as linker between the carbazole and the ppy ligand (Scheme 1).
We found that the ethynyl ligand was oxidized to keto structure
during the metalation of the ligands with K2PtCl4. All the complexes
show intensive room temperature phosphorescence in fluid solu-
tion. Red-shifted emission wavelength was found for the complexes
(ca. 550 nm), compared tothe parent complex ppyPt(acac) (486 nm).
Greatly improved phosphorescence property were found for Pt-3
compared to the parent complex ppyPt(acac). The luminescent O2
sensing properties of these complexes in polymer films were also
studied. Our systematic study on the photophysical properties and
the O2 sensing properties of the cyclometalated Pt(II) complexes
may prove useful for future development of the phosphorescent
cyclometalated Pt(II) complexes.
parent complex of ppyPt(acac) (
l
em ¼ 486 nm) [3].
40-bromo-ppy was obtained by a feasible approach [29]. The
bromo substitution at ppy allows further derivatization of the ligand,
suchaswithSonogashiraorNegishicouplingreactions(Scheme 1).N-
butyl ethynylated carbazole was prepared and reacted with 40-bromo
ppy via the Sonogashira coupling reaction. We prepared ligand L2
with the 3-iodo-6-bromo carbazole. Reaction of K2PtCl4 with HC^N
ligand precursor (substituted ppy) forms the chloride-bridged dimer,
C^N Pt(m-Cl)2PtC^N, which is then cleaved with acetyl acetone to give
the corresponding monomeric C^N Pt(O^O) complex.
For Pt-1 and Pt-2, however, the desired ethynyl structures were
not obtained. Instead, the products were proved to be the a-diketo
structure (Scheme 1). This is proved by the 13C NMR data
(185.72 ppm, 184.23 ppm for Pt-1 and 196.53, 196.38, 195.38, 43.24
for Pt-2, respectively). Further evidence is from the high resolution
mass spectra, for which m/z ¼ 725.1911 and 843.0262 were observed
for the Pt-1 and Pt-2, respectively. This is due to the Pt catalyzed
oxidation reaction during the metalation procedure of the ethynyl
ligand with K2PtCl4 [30]. For Pt-2, gCOSY, TOCSYand gHMBC spectra
were also measured to validate the proposed molecular structures
(see Figs. S16eS18 in Supporting information).
2. Results and discussions
2.1. Synthesis
The design rationale of the ligand lies on the notion that by
attachment of an electron pushing group to the ppy ligand will
Scheme 1. Synthesis of the cyclometalated Pt(II) complexes Pt-1, Pt-2 and Pt-3. (a) NaNO2/HCl, NaCO3; (b) BuBr, NaH, r.t.; (c) trimethylsilylacetylene, Pd(PPh3)2Cl2, PPh3, CuI, NEt3,
reflux; K2CO3/methanol; (d) 4, Pd(PPh3)4, CuI, toluene/(i-Pr)2NH, reflux; (e) i: K2PtCl4, ethoxyethanol/water, ii: Hacac, Na2CO3, ethoxyethanol; (f) NBS, r.t.; (g) 1-ethynylbenzene,
Pd(PPh3)4, CuI; (h) 4, n-BuLi, ZnCl2, 78 ꢁC.

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W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
a
b
Fig. 1. UVevis absorption of (a) the ligands and (b) the complexes. 1.0 ꢂ 10ꢀ5 mol dmꢀ1 in CH2Cl2. 20 ꢁC.
2.2. UVevis absorption of the ligands and the cyclometalated Pt
complexes
ligand, where the HOMO is localized [3,31,33]. As a result, the
energy level of the HOMO will increase, but the energy level of the
LUMO is unaffected. Thus decreased HOMO-LUMO energy gap is
resulted and red-shifted emission will be expected [3,31,34].
Notably, Pt-3 shows much longer phosphorescence lifetime
The absorption bands of ligand L3 were below 370 nm (Fig. 1a).
These absorptions were assigned to the transitions involving the
carbazole related
absorptions of L1 and L2 are due to the extended
the ligand.
Compared to the free ligands, the complexes show red-shifted
absorption (Fig.1b). The new weak absorption at 420 nm with molar
extinction coefficients in the range of 0.473e1.01 ꢂ 104 cmꢀ1
molꢀ1 dm3, are due to the allowed S0 / 1MLCT and the S0 / 1ILCT
transitions [3,31]. The absorptions below 350 nm are due to the p-p
*
transition of the C^N fragment.
p
-conjugation system. The relatively red-shifted
(
sP ¼ 12.4
m
s) and much higher phosphorescence quantum yield
p-conjugation of
(FP ¼ 66%) than ppyPt(acac), which gives sP ¼ 2.6
ms and FP ¼ 15%,
respectively [31]. We attribute the enhanced phosphorescence of
Pt-3 to the strengthened ligand field, due to the electron-donating
carbazole moiety. Thus the non-radiative decay channel of 3MC
state will be elevated to be much higher above the emissive
3MLCT/3IL state [3]. Previously Ir(III) complexes with the carbazole
moiety directly cyclometalated were reported, but those Ir(III)
complexes show much shorter phosphorescence lifetimes and
much lower quantum yields [6].
We demonstrate that direct metalation of the carbazole moiety
is not necessary for long emission wavelength, thus more diverse
chromophores could be used in preparation of the complexes
which give red-shifted emission, vs. ppyPt(acac) [3,31,35]. This
emission wavelength tuning strategy for the cyclometalated Pt(II)
(acac) complex may prove significant for development of novel
electroluminescent materials. It should be pointed out that triplet
emitter Pt-3 is multifunctional, as carbazole moiety is incorporated
in the complexes, which is known as a good hole transporter
[34,35], thus this complex could be used as OLED material.
Interestingly, different emission profiles were observed for
complexes Pt-1 and Pt-2. The emission bands at 554 nm and
556 nm are not well-resolved, which is different from that of Pt-3
(Fig. 2). Furthermore, initially we suppose that Pt-1 and Pt-2 will
2.3. Emission of the ligands and the Pt complexes
The emissions of the ligands and complexes were studied
(Fig. 2). The emission of the ligands is in agreement with the extent
of the
largest
p
p
-conjugation of the ligands. For example, L2 shows the
-conjugation framework, correspondingly, this ligand
shows the longest emission wavelength. The opposite was
observed for L3 [32].
With metalation, Pt-3 shows red-shifted emission at 540 nm,
which is due to the 3MLCT/3ILCT transitions of the C^N Pt (acac)
compounds [3,31]. Note the emission wavelength is red-shifted by
about 54 nm compared to ppyPt(acac) (
red-shifted emission can be rationalized by the attachment of the
l
em ¼ 486 nm) [31]. The
electron-donating carbazole moiety to the phenyl group of the ppy
a
b
Fig. 2. Emission spectra of the ligands and the Pt(II) complexes. The emission intensity of the complexes is not comparable. 1.0 ꢂ 10ꢀ5 mol dmꢀ3 in CH2Cl2, r. t. (a) L1:
ex ¼ 370 nm,
l
L2:
l
ex ¼ 360 nm, L3:
l
ex ¼ 350 nm. (b) Pt-1:
l
ex ¼ 370 nm, Pt-2:
l
ex ¼ 364 nm, Pt-3: ex ¼ 350 nm. The asterisk (*) in b indicates the second order transition of the
l
monochromator of the fluorescence spectrometer.

W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
2391
Table 1
Photophysical properties of the ligands and the Pt(II) complexes.
Compounds
labs/nma
e
/104 cm-1 mol1dm3
Emission
a
d
lem
s
F
I0/I100
Ligand 1
Ligand 2
Ligand 3
Pt-1
Pt-2
Pt-3
305/338
311/342
302/323
277/298/335
264/292/337
300/331/348
3.48/3.38
5.71/4.29
3.88/2.97
5.18/5.02/2.95
5.54/4.74/2.90
4.10/3.12/3.06
426
422
410
554
556
540
1.38 ns
3.16 ns
1.77 ns
0.75b
0.56b
0.62b
0.13c
0.20c
0.66c
1.2
1.3
1.2
10.1
11.6
71.1
1.86
2.82
m
m
s
s
m
12.40
s
a
Result of compound in deaerated DCM solution (1.0 ꢂ 10ꢀ5 mol dm-3). In solution of CH2Cl2, 298 K.
b
c
Result of deaerated solution, with compound quinine as the standard (
F
¼ 0.547 in 0.05 M sulphuric acid).
Result of deaerated solution, with complex Pt(tBu2bpy)(C^CePh)2
(
F
¼ 0.496 in MeCN) as the standard.
d
I0 is the emission intensity under N2 atmosphere and I100 is the emission intensity under O2 atmosphere.
show blue-shifted emission, due to the electron-withdrawing
diketo moiety on the phenyl group of the ppy ligand, where HOMO
is localized [31]. To our surprise, Pt-1 and Pt-2 show red-shifted
emission bands in the range of 500 nme700 nm (the phospho-
rescence emission band), the phosphorescent lifetime is in the
range of 1.86 mse12.4 ms.
emission compared to ppyPt(acac) (
l
em ¼ 486 nm). The emission
wavelength of Pt-1 and Pt-2 are even longer than the emission of
Pt-3. This observation is in stark contrast to the accepted knowl-
edge that ppyPt(acac) complex will show blue shift emission given
that an electron-withdrawal moiety is attached to the phenyl group
2.4. DFT/TDDFT calculation of the complexes: the electronic
structure of the low-lying excited states
of the ppy ligand [3,31,34]. As the a-diketo is electron-withdrawal,
Recently DFT methods have been used to study the photo-
physical properties of the singlet and triplet emitters [20,36ꢀ40].
The photophysics of luminophores can be better understood by
revealing the molecular orbitals of the electronic transitions of the
luminophore, this is beneficial for the future design of lumino-
phores with predetermined photophysical properties [20,40].
Firstly Pt-3 was studied with the DFT calculations. The dihedral
angle between the carbazole moiety and the ppy moiety was
observed as 37ꢁ for the optimized ground state geometry (Fig. 3).
The optimized bond length are PtꢀN (2.024 Å), PtꢀC (1.986 Å) and
PtꢀO (2.04e2.15 Å), respectively. The bond angles of CePteN
(81.2ꢁ) and OePteO (90.6ꢁ), are in good agreement with the single
crystal structure of the related cyclometalated Pt complexes [31].
We found the electron-rich carbazole moiety contributes
significantly to the HOMO, while the LUMO is predominantly
localized on the pyridine/phenyl groups of the ppy ligand (Fig. 3).
The Pt atom contributes slightly to the MOs. These MOs can be
used to rationalize the red-shifted emission of the complexes
compared to the parent complex ppyPt(acac). The energy level of
HOMO will be increased with the electron-donating carbazole
fragment appended at the phenyl group of the ppy ligand
(ꢀ5.06 eV), vs. the HOMO energy of ꢀ5.42 eV for ppyPt(acac). Both
Pt-3 and ppyPt (acac) share similar LUMO energy level of ꢀ1.55 eV
and ꢀ1.58 eV, respectively. Thus the energy gap between HOMO
thus we propose the diketo moiety in Pt-1 and Pt-2 may be
involved in the LUMO orbit and acts as an electron sink, i.e. the
electronic structure of the emissive state may be different from the
typical 3MLCT/3IL excited state of the normal ppyPt(acac)
complexes, featured with phenyl / pyridine charge transfer [3,31].
The LUMO of the complexes Pt-1 and Pt-2 will be stabilized with
this electron-withdrawal moiety thus the energy gap of the HOMO-
LUMO may be decreased, as a result, the emission may show
bathochromic shift compared to ppyPt(acac) [21e25].
The emission intensity of the complexes can be significantly
quenched by O2. This result also supports the triplet nature of the
emissions, as well as long phosphorescence lifetimes. Our strategy
of using an electron sink to perturb the electronic structure of the
T1 excited state to tune the emission property may prove useful for
preparation of new cyclometalated Pt complexes as electrolumi-
nescent materials. The electron-withdrawal diketo moiety may
serve as the electron-transporting moiety for these multifunctional
materials. Furthermore, the use of electron-donating carbazole to
increase the phophorescence quantum yield and prolong the
phosphorescence lifetime is useful for design of new phosphores-
cent cyclometalated complexes.
The photophysical parameters of the ligands and the cyclo-
metalated Pt(II) complexes were compiled in Table 1. For the
Fig. 3. Frontier molecular orbitals for Pt-3. calculated by DFT/TDDFT at the B3LYP/6-31G(d)/LanL2DZ level using Gaussian 09.

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W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
Table 2
Table 3
Electronic excitation energies (eV) and corresponding Oscillator strengths (f), main
configurations and CI coefficients of the Low-lying electronically excited states of
complex Pt-3, calculated by TDDFT//B3LYP/6-31G(d)/LanL2DZ, based on the DFT//
B3LYP/6-31G(d)/LanL2DZ Optimized ground state geometries.
Electronic excitation energies (eV) and corresponding oscillator strengths (f), main
configurations and CI coefficients of the Low-lying Electronically excited states of
complex Pt-1, Calculated by TDDFT//B3LYP/6-31G(d)/LanL2DZ, based on the opti-
mized ground state geometries.
Electronic
transition
TDDFT//T//B3LYP/6-31G(d)
Electronic
transition
TDDFT//B3LYP/6-31G(d)
Energya
fb
Compositionc
CId
Character
ILCT
Energya
fb
Compositionc
CId
Character
MLCT
S0 / S1
3.03 eV/
409 nm
0.2209
H / L
0.5588
S0 / S1
2.73 eV/
455 nm
0.0020
Hꢀ5 / L
0.1108
Hꢀ3 / L
Hꢀ1 / L
Hꢀ1 / L
0.1817
0.3279
0.5753
LLCT, MLCT
LLCT, MLCT
LLCT, MLCT
Hꢀ4 / L
0.4079
0.1751
0.4048
0.1627
MLCT
ILCT
ILCT
Hꢀ4 / L þ 1
Hꢀ2 / L
S0 / S2
3.24 eV/
383 nm
0.1953
S0 / S2
2.85 eV/
435 nm
0.0502
0.1360
Hꢀ3 / L
LLCT
H / L
Hꢀ4 / L
0.3618
0.6924
ILCT
MLCT
S0 / S3
S0 / S6
3.47 eV/
357 nm
3.68 eV/
336 nm
0.0050
0.1413
Hꢀ2 / L
H / L
Hꢀ6 / L
0.1331
0.6098
0.1879
ILCT
MLCT
LLCT
Hꢀ3 / L
0.3660
LLCT, MLCT
S0 / S10
3.76 eV/
330 nm
Hꢀ2 / L
Hꢀ1 / L
Hꢀ1 / Lþ1
H / Lþ1
H / L þ 3
Hꢀ5 / L
0.2603
0.1099
0.2088
0.4244
0.1552
0.1774
ILCT
Hꢀ2 / L þ 1
Hꢀ1 / L þ 1
H / L þ 2
0.1661
0.5234
0.2556
0.4316
0.1383
ILCT
ILCT
LLCT
LLCT
MLCT
LLCT, MLCT
MLCT, ILCT
LLCT, ILCT
ILCT, MLCT
ILCT, LLCT
Hꢀ3 / L þ 2
Hꢀ5 / L
S0 / T1
2.27 eV/
545 nm
0.0000e
S0 / T1
2.47 eV/
502 nm
0.0000e
Hꢀ4 / L
Hꢀ4 / L þ 1
Hꢀ2 / L
Hꢀ2 / L þ 1
Hꢀ1 / L
H / L
0.3863
0.2242
0.4391
0.2119
0.1059
0.1497
ILCT
MLCT
ILCT
ILCT
ILCT
Hꢀ3 / L
Hꢀ2 / L
Hꢀ1 / L
H / L
0.2280
0.1252
0.2460
0.5847
0.1321
LLCT, MLCT
ILCT
LLCT, MLCT
ILCT
H / L þ 1
ILCT
MLCT
a
a
Only the selected low-lying excited states are presented.
Oscillator strength.
H stands for HOMO and L stands for LUMO. Only the main configurations are
Only the selected low-lying excited states are presented.
Oscillator strength.
H stands for HOMO and L stands for LUMO. Only the main configurations are
b
c
b
c
presented.
presented.
d
d
The CI coefficients are in absolute values.
The CI coefficients are in absolute values.
e
e
No spin-orbital coupling effect was considered, thus the f values are zero.
No spin-orbital coupling effect was considered, thus the f values are zero.
and LUMO of complex Pt-3 was reduced to 3.51 eV, vs. the 3.84 eV
of ppyPt(acac) (see Supporting information).
ground state geometries (Table 2). The calculated excitation energies
are 409 nm, 383 nm, 336 nm, etc. These values are in good agreement
with the experimental result of the UVevis absorption spectra, which
show absorption at 400 nm, 350 nm, 328 nm, etc (Fig. 1). The T1 state
was also studied in order to reveal the emissive property of the
complex. We found the main component of the T1 state is the
HOMO / LUMO transition. These results clearly demonstrated that
the involvement of the carbazole moiety in the T1 state of the
complex, which is responsible for the different emission property
compared to ppyPt(acac). The calculated energy level of T1 state is
502 nm, which is in line with the experimental results (540 nm). Thus
the red-shifted emission of the complex Pt-3 can be rationalized by
Compared to ppyPt(acac), the contribution of Pt(II) ion to the
HOMO and LUMO are significantly reduced in complex Pt-3 (see
Supporting information for the MOs of ppyPt (acac)). Thus we
propose the 3IL is more prominent in the emissive state (mixed
3MLCT and 3LC) and the phosphorescent lifetime of the Pt
complexes is expected to be longer [31]. This is fully supported by
the experimental results that phosphorescent lifetime of 12.4
ms
was observed for Pt-3, vs. lifetime of 2.6 s for ppyPt (acac) [31].
m
The electronic structure of the low-lying electronic transitions
were studied with the TDDFT method, based on the optimized
Fig. 4. Frontier molecular orbitals for Pt-1. calculated by DFT/TDDFT at the B3LYP/6-31G(d)/LanL2DZ level using Gaussian 09.

W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
2393
Fig. 5. Spin density surface of the complexes Pt-1, Pt-2 and Pt-3. Calculated based on the optimized geometry of the lowest-lying triplet state. The molecular structure of Pt-2 is
presented for clarity.
attachment of the electron-donating carbazole moiety at the phenyl
group of the ppy ligand (where HOMO is localized).
As close analogs to Pt-3, the a-diketo containing complexes Pt-1
and Pt-2 were also studied with the DFT/TDDFT calculations (Fig. 4
and Supporting information). The result indicates a trans skewed
with the ppy or the carbazole moiety to which it was attached,
respectively. The optimized coordination angle OePteO and
CePteN is 90.7ꢁ and 81.1ꢁ, respectively. The bond length of CꢀPt
and NꢀPt is 1.98 Å and 2.02 Å, respectively. The optimized bond
length OꢀPt is in the range of 2.04 Åe2.15 Å. These values are close
to the single crystal structures of the related cyclometalated Pt(II)
(acac) complexes [34].
conformation for the a-diketo moiety [41], with torsion angle of
123.2ꢁ. However, both carbonyl groups take a coplanar geometry
a
b
c
d
Fig. 6. Phosphorescent intensity response of sensing films of the complexes in IMPEK-C to step variations of O2 concentrations. (a) response of complex Pt-1 to switch between neat
N2 and O2. em ¼ 542 nm. (b) dynamic response of complex Pt-1 to variation of the oxygen concentrations of N2/O2 mixed gas. ex ¼ 370 nm, em ¼ 542 nm. (c)
ex ¼ 370 nm,
response of complex Pt-3 to switch between neat N2 and O2. em ¼ 536 nm. (d) dynamic response of complex Pt-3 to variation of the oxygen concentrations of N2/O2
ex ¼ 370 nm,
mixed gas. em ¼ 536 nm.
ex ¼ 370 nm,
l
l
l
l
l
l
l
l

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W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
is ꢀ5.55 eV and ꢀ2.12 eV, respectively. Thus the energy gap
between the HOMO and LUMO is
EHOMOeLUMO ¼ 3.43 eV, by
comparison ppyPt(acac) of ꢀ5.42 eV and ꢀ1.58 eV, respectively
EHOMOeLUMO ¼ 3.84 eV). Thus the red-shifted emission of the Pt-1
can be rationalized by the electron sink effect of the -diketo
D
(D
a
moiety, by which the energy level of the LUMO of the complex is
decreased, but the energy level of the HOMO orbit is almost unaf-
fected, a decreased HOMO-LUMO energy gap is obtained.
In order to study the phosphorescence origin of the complexes,
the spin density surfaces of the triplet excited states of the
complexes were investigated (Fig. 5). For Pt-1 and Pt-2, the spin
density is mainly localized in the 1,2-dione moieties. For Pt-3,
however, the spin density in localized on the ppy ligand and the Pt
center. Drastically different spin density distribution of the Pt-1, Pt-
2 and Pt-3 indicate different photophysical properties of these
complexes. These theoretical predictions are in agreement with the
experimental results, which indicate similar phosphorescence
lifetimes and phosphorescence quantum yields for Pt-1 and Pt-2,
but different photophysical properties for Pt-3 (Table 1).
Fig. 7. Oxygen sensitivity of the emission of the complexes Pt-1, Pt-2 and Pt-3. The
fitting according to Eq. (2) of the oxygen sensing data in Fig. 6 and Fig. S30 in
Supporting information.
Our results show that the photophysical properties of the
cyclometalated Pt complexes, such as the UVevis absorption, can
be studied with the DFT/TDDFT calculations. Our theoretical
revealing the photophysics of the metalated complexes may prove
useful for future design of the cyclometalated Pt complexes with
red-shifted emission compared to ppyPt(acac).
For Pt-1, the first calculated absorption bandis at 436 nm(S2 state,
with much higher oscillator strength than the S1 state). This
absorption is assigned as the 1MLCT/1IL transition (phenyl / pyri-
dine and Pt / ppy charge transfer), which is in good agreement with
the experimental results in the UVevis absorption spectra. Excita-
tions to higher singlet states were also calculated (Table 3). Calcula-
tions indicated that carbazole was involved in the transitions. It
should be pointed that the a-diketo moiety was involved in the
2.5. Luminescent oxygen sensing properties of the cyclometalated
Pt complexes
LUMO, this result infers that the diketo may act as electron trap
(strong electron acceptor). Basically the excitation energies are
consistent with the UVevis absorption spectra (Fig. 1).
We have demonstrated that the complexes show phosphores-
LUMOþ1 and LUMOþ2 were involved in these excitations and
the diketo serves as electron trap in these molecular orbits (Fig. 4).
We noticed that S1 state is featured with smaller f value than the S2
state. This is probably due to the charge transfer feature of the S1
state (carbazole / ppy) [42].
cence with lifetimes in the range of
ms (Table 1), which ensure
efficient quenching of the emission by O2 [1,2,20e25].
First we compared the response of the emission of the complexes
Pt-1, Pt-2 and Pt-3 in solution to the variation of the O2 partial
pressure (See Supporting information). For Pt-1, the emission
intensity is quenched by ca. 78.7% in air compared to the emission
under N2. In O2, the emission intensity was quenched by 95.2% of the
initial value that under N2 (see Supporting information).
Pt-3 was also studied under similar condition (see Supporting
information). We found the emission at 540 nm is highly sensi-
tive to O2. The emission was almost completely quenched in air (ca.
21% O2 v/v). Thus we propose the phosphorescence lifetime of Pt-3
is much longer than that of Pt-1 (Table 1), which is supported by
In order to study the emissive state of the complex, the T1 state
is investigated with the TDDFT calculations and the electronic
structure of T1 state is listed in Table 3. carbazole / ppy and
Pt / ppy charge transfer are involved in the T1 state, thus the T1
state can be described as 3MLCT/3IL mixed state.
a-diketo moiety
was involved in the orbitals such as LUMO, LUMO þ 1 and
LUMO þ 3, which are involved in the T1 state. Therefore, we
conclude that
a-diketone acts as electron sink and the emissive
state of the complex Pt-1 is different from the typical ppyPt(acac)
complexes. The calculated energy level of T1 state (545 nm) is close
to the experimental results (554 nm).
the experimental result that a lifetime of 12.4
ms was observed for
Pt-3, vs. the much shorter lifetime of 1.86 s for Pt-1.
m
SterneVolmer quenching equation (Eq. (1)) can be used to
quantitatively describe the luminescence O2 sensing, Where I0
stands for emission intensity in inert atmosphere, I is the emission
intensity under specific O2 partial pressure, kq is the quenching
constant, s0 is the unquenched lifetime and [Q] is the concentration
of quencher. The longer the triplet excited state lifetime of a dye,
the more sensitive of its emission to O2.
Based on the frontier molecular orbitals, we found the
a-diketo
moiety is involved in the LUMO. The -diketo moiety is electron
a
deficient thus we expect the energy level will be decreased but the
HOMO is nearly unaffected. Therefore we expected red-shifted
emission wavelength for Pt-1 than that of ppyPt(acac). The DFT
calculations indicate the energy levels of HOMO and LUMO of Pt-1
Table 4
Parameters of O2 sensing film of complexes Pt-1, Pt-2 and Pt-3 with IMPEK-C as supporting matrix (fitting result of the two-site model).
KSV1b/Torrꢀ1
KSV2b/Torrꢀ1
r2c
KSV app d/Torrꢀ1
pO2e/Torr
a
a
f1
f2
Pt-1
Pt-2
Pt-3
0.493
0.271
0.512
0.507
0.729
0.488
0.012
0.012
0.047
0.0002
0.0001
0.0001
0.9992
0.9989
0.9993
0.0058
0.0032
0.0238
86.9
86.2
21.5
a
The ratio of the two portion of the dyes.
The quenching constants of the two portions.
The determination coefficients.
b
c
d
e
app
Weighted quenching constant, KSV
¼ f1ꢂ KSV1 þ f2 ꢂ KSV2
.
The oxygen partial pressure at which the initial emission intensity of film is quenched by 50%, and can be calculated as 1/KSV
.

W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
2395
I0
I
photophysical properties of the complexes were studied with
experimental and theoretical methods. Oxidation of the ethynyl
¼ 1 þ kqs0½Qꢃ
(1)
bond to a-diketo or methylene-keto structure were found for the
For the heterogeneous O2 sensing films, however, modified
metalation of the ethynyl ligands with K2PtCl4. Red-shifted emis-
sions were observed for both the complexes with electron-
donating (Pt-3) and electron-withdrawal groups (Pt-1 and Pt-2)
attached to ppy. Pt-3 gives intensive room temperature phospho-
rescence with emission band at ca. 540 nm (FP ¼ 0.66) and pro-
SterneVolmer or two-site model is required to study the quenching
effect [7e10], because even in “homogenous” polymers, the dye
molecules still dwell in different microenvironments. In the two-
site model, the O2-responsive dyes are treated as two different
portions. Fraction of the two portions are defined as f1 and f2,
respectively (f1 þ f2 ¼ 1), the two portions show different
quenching constants (KSV1 and KSV2, Eq. (2)).
longed phosphorescence lifetime (sP ¼ 12.4
m
s) compared to the
s).
model complex ppyPt(acac) (
lem ¼ 486 nm, FP ¼ 0.15, sP ¼ 2.6
m
Based on the DFT calculations, we propose the red-shifted emission
I0
I
1
of Pt-3 is due to the increased energy level of the HOMO, whereas
the a-diketo is involved in the LUMO of Pt-1and Pt-2 and as a result
¼
(2)
f1
f2
þ
the energy level of LUMO is decreased. In both cased the energy gap
between the HOMO and the LUMO is decreased compared to the
model complex ppyPt(acac). Thus the emissive states of Pt-1 and
Pt-2 are different from the typical 3MLCT/3IL (Pt / ppy and
phenyl / pyridine) of the normal ppyPt(acac) complexes. The
complexes were used for luminescent oxygen sensing. Pt-3 shows
the highest quenching constant (KSV ¼ 0.0238 Torrꢀ1), which is 6.8-
fold of a reported cyclometalated Ir(III) complex used for lumi-
nescent oxygen sensing.
1 þ KSV1pO
1 þ KSV2pO
2
2
For practical O2 sensor, the O2 sensing property should be
studied in solid matrix, such as polymer, or inorganic porous
material [1,2]. The supporting matrix should ensure a fast response
time (tY95, the time that elapsed before 95% of luminescence
intensity change finished after switching the gas from N2 to O2) and
recovery time (t[95, the time elapsed before 95% of luminescence
intensity change finished after switching the gas from O2 to N2)
[20e25]. Usually porous materials, such as MCM-41, are required to
achieve a fast response vs. the variation of the O2 partial pressures
(concentration) [43,44]. Recently we found a specially designed
aromatic polymer, IMPEK-C, with high oxygen permeability and
diffusion coefficients, which is ideal for luminescent O2 sensing
matrix [20e25]. Therefore, the O2 sensing properties of Pt-1 and
Pt-3 were studied in the polymer film of IMPEK-C [45]. The films
were prepared by the dissolution-casting method.
Firstly the O2 sensing films were tested against O2 and N2
saturation cycles (Fig. 6a and c). The response time is as short as
3.3 s, and the recovery time is as short as 3.7 s [20,21]. Such fast
response and recovery time are adequate for most applications. Fast
response can usually be achieved with porous materials, such as
MCM-41 [43,44,46ꢀ48]. Our solution-casting approach is straight
forward (see experimental for oxygen sensing films preparation),
thus can be used to easily fabricate reliable luminescent oxygen
sensors.
Next, we examined the dynamic response of the sensing films
of Pt-1 and Pt-3 vs. small steps variation of the O2 partial pres-
sure. Using this kind of test and the numeric fitting of the
response with the two-site model, the O2 sensing property of the
complexes can be compared quantitatively. Pt-3 is more sensitive
to O2 (Fig. 6d). With 3.5% O2 (v/v), the emission intensity was
quenched by 54.6%. Under the same condition, the sensing film of
Pt-1 only shows 24.8% quenching (Fig. 6b). Furthermore, the
reversibility of the phosphorescence response in Fig. 6 demon-
strated the good photostabilities of the complexes and the
sensing films.
4. Experimental
4.1. General procedures, materials and physical measurements
The general procedure for the preparation is given in Scheme 1.
All the chemicals are analytical pure and were used as received
without further purification. NMR spectra were taken on
a 400 MHz Varian Unity Inova spectrophotometer. Mass spectra
were recorded with Q-TOF Micro MS spectrometer. UVevis spectra
were taken on an HP8453 UVevisible spectrophotometer. Fluo-
rescence spectra were recorded on a JASCO FP-6500 or a Sanco 970
CRT spectrofluorometer. Phosphorescence quantum yields were
measured with complex Pt(tBu2bpy)(C^CePh)2
MeCN) as the reference [49]. Luminescence lifetimes were
(F
¼ 0.496 in
measured on
instrument.
a Horiba Jobin Yvon Fluoro Max-4 (TCSPC)
The structures of the complexes were optimized using density
functional theory (DFT) with B3LYP functional and 6-31G(d)/
LanL2DZ basis set. 6-31G(d) basis set were employed for C, H, N, O
and LanL2DZ basis set was used for Pt(II). The excited state related
calculations were carried out with the time dependent DFT (TDDFT)
based on the optimized ground state geometry. The spin density
surfaces of the complexes were calculated based on the optimized
geometry of the T1 excited states. All these calculations were per-
formed with Gaussian 09 [50].
The sensing data were fitted with two-site model (Eq. (2))
(Fig. 7). The Ksv value of Pt-3 is much higher than that of Pt-1 and
Pt-2 (Table 4). We noticed the Ksv of Pt-3 is 6.8-fold of a recently
4.2. Synthesis
4.2.1. 9-Butyl-3-iodocarbazole (2)
reported cyclometalated Ir(III) complex (
s
¼ 4.3
ms in inert atmo-
n-C4H9Br (1.48 mL, 13.8 mmol) were added to a solution of
compound 1 (4.0 g, 13.7 mmol) in DMF (30 mL). Then, NaH (70 wt.%
in mineral oil, 960.0 mg, 28 mmol) was added in portions. The
mixture was stirred at room temperature until the reaction was
completed (monitored by TLC). The reaction mixture was poured
into water (200 mL), the precipitate was collected by filtration, and
purified with column chromatography (silica gel, petroleum
ether:DCM ¼ 1:1, v/v) to give 3.52 g white solid. Yield: 73.8%. 1H
NMR (400 MHz, CDCl3): 8.40 (s, 1H), 8.04 (d, 1H, J ¼ 7.6 Hz), 7.71 (d,
1H, J ¼ 10.1 Hz), 7.51 (t,1H, J ¼ 7.3 Hz), 7.41 (d,1H, J ¼ 8.2 Hz), 7.24 (t,
1H, J ¼ 7.3 Hz), 7.20 (d, 1H, J ¼ 8.4 Hz), 4.26 (t, 2H, J ¼ 7.3 Hz),
1.87e1.80 (m, 2H,), 1.43e1.33 (m, 2H), 0.94 (t, 3H, J ¼ 7.3 Hz).
sphere) with diphenylamine caped ppy ligand (it should be pointed
out that the supporting matrix for the Ir complex is ethyl cellulose)
[11]. However, the Ksv values of the Pt(II) complexes described
herein are lower than the metalloporphyrins, such as PtOEP,
complexes with much longer lifetimes (>50 ms) [21].
3. Summary
Carbazole capped ppyPt(acac) complexes with linkers of
-diketo (Pt-1 and Pt-2) and CeC single bond (Pt-3) between the
a
carbazole and the ppy group were synthesized and the

2396
W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
4.2.2. 9-Butyl-3-ethynylcarbazole (3)
precipitate was used to react with Hacac (43.7 mg, 0.437 mmol) in
the presence of Na2CO3 (154.2 mg, 0.437 mmol) in 2-ethoxyethanol
(16 mL) at 100 ꢁC for 16 h. The reaction mixture was then poured
into water, the precipitate was purified with column chromatog-
raphy (silica gel, eluting with CH2Cl2) to afford the product as
yellow solid (50.0 mg), yield: 24.8%. 1H NMR (400 MHz, CDCl3)：
9.04 (d, 1H, J ¼ 5.7 Hz), 8.73 (s, 1H), 8.28 (s,1H), 8.14 (t, 2H,
J ¼ 8.7 Hz), 7.87 (t, 1H, J ¼ 7.7 Hz), 7.75 (d, 1H, J ¼ 7.9 Hz), 7.68 (d, 1H,
J ¼ 8.0 Hz), 7.52e7.49 (m, 2H), 7.45 (d, 2H, J ¼ 7.5 Hz), 7.31 (d, 1H,
J ¼ 7.5 Hz), 7.22 (t, 1H, J ¼ 6.1 Hz), 5.44 (s, 1H), 4.35(t, 2H, J ¼ 7.1 Hz),
2.00 (s, 3H), 1.91 (s, 3H), 1.88e1.82 (m, 2H), 1.44e1.34 (m, 2H), 0.96
Under Ar atmosphere, compound 2 (2.8 g, 8.0 mmol), Pd
(PPh3)2Cl2 (103.2 mg, 0.16 mmol), PPh3 (83.0 mg, 0.3 mmol), CuI
(15.2 mg, 0.08 mmol) were dissolved in NEt3 (30 mL). After stirring
for 5 min, ethynyltrimethylsilane (1.4 mL, 9.6 mmol) was added via
syringe. The solution was refluxed for 8 h. The solvent was removed
under reduced pressure and the crude product was purified by
column chromatography (silica gel, dichloromethane/petroleum
ether ¼ 1:4, v/v), brown solid was obtained. The above trime-
thylsilane protected intermediate was dissolved in methanol
(30 mL), K2CO3 (1.2 g) was added and the mixture was stirred at r.t.
for 3 h. The solvent was removed under reduced pressure. Water
was added and the mixture was extracted with CH2Cl2. The organic
layer was dried over anhydrous Na2SO4. After removal the solvent,
compound 3 was obtained as light yellow solid. 620.0 mg, yield:
34.0%. 1H NMR (400 MHz, CDCl3) 8.24 (s,1H), 8.04 (d,1H, J ¼ 7.8 Hz),
7.57 (d, 2H, J ¼ 8.4 Hz), 7.44 (t, 1H, J ¼ 7.8 Hz), 7.36 (d, 1H J ¼ 8.1 Hz),
7.28 (d, 1H J ¼ 8.4 Hz), 7.23e7.19 (m, 1H), 4.20 (t, 2H J ¼ 7.2 Hz), 3.05
(s, 1H), 1.82e1.74 (m, 2H), 1.38e1.29 (m, 2H), 0.90 (t, 3H J ¼ 7.3 Hz).
(t, 3H, J ¼ 7.3 Hz). 13C NMR (100 MHz, CDCl3)
d 196.79, 195.27,
186.07, 184.73, 184.65, 166.86, 150.94, 147.99, 144.33, 141.44, 139.70,
138.58, 133.12, 131.87, 127.83, 126.90, 125.86, 125.12, 124.03, 123.36,
122.99, 121.20, 120.60, 119.88, 109.55, 109.10, 102.73, 43.39, 31.25,
29.90 28.36, 27.16, 20.70, 14.01. MALDI-HRMS ([C34H30N2O4Pt]ꢀ)
calcd 725.1853, found 725.1911.
4.2.6. 3-Bromo-9-butyl-6-iodocarbazole (5)
Under argon atmosphere, the solution of N-bromosuccinimide
(NBS) (1.02 g, 5.73 mmol) in 6.0 mL DMF was added dropwise to
a solution of compound 2 (2.0 g, 5.73 mmol) in DMF (6 mL). The
mixture was heated at 60 ꢁC for 6 h and then cooled to r.t., the
reaction mixture was then poured into water, and the precipitate
was collected, washed with water and dried. Pale solid (1.20 g) was
obtained, yield: 44.7%. 1H NMR (400 MHz, CDCl3): 8.33 (d, 1H,
J ¼ 1.3 Hz), 8.13 (d, 1H, J ¼ 1.5 Hz), 7.72e7.69 (m, 1H, J ¼ 8.6 Hz),
7.56e7.53 (m, 1H, J ¼ 8.7 Hz), 7.27 (t, 1H, J ¼ 4.7 Hz), 7.19 (t, 1H,
J ¼ 8.5 Hz), 4.25 (t, 2H, J ¼ 7.1 Hz), 1.84e1.76 (m, 2H), 1.37e1.31 (m,
2H), 0.94 (t, 3H, J ¼ 7.3 Hz).
4.2.3. 2-(4-Bromophenyl) pyridine (4)
At 0 ꢁC, an aqueous solution of NaNO2 (4.14 g, 0.06 mmol, 7.5 mL
of 8.0 M solution, 2 equivalent) was slowly added to a suspension of
p-bromoaniline (5.00 g, 30 mmol, 1 equivalent) in concentrated HCl
(10 mL). The mixture was stirred at 0 ꢁC for 1 h and was carefully
added into pyridine (125 mL) by dropwise. The brown solution was
stirred at 40 ꢁC for 4 h and then Na2CO3 (50.0 g) was added and the
slurry was stirred for 18 h. The reaction mixture was extracted with
CH2Cl2 (3 ꢂ 50 mL) and the combined organic layers were dried
over anhydrous Na2SO4 and evaporated to dryness. The crude
product was purified with column chromatography (silica gel,
CH2Cl2 as the eluent). Orange solid was obtained, 2.58 g, yield:
37.0%. 1H NMR (400 MHz, CDCl3) 8.68 (d, 1H, J ¼ 4.0 Hz), 7.86 (d, 2H,
J ¼ 8.4 Hz), 7.77 (t, 2H, J ¼ 6.4 Hz), 7.73 (d, 1H, J ¼ 8.4 Hz), 7.58 (d, 2H
J ¼ 8.4 Hz), 7.25 (t, 1H, J ¼ 6.0 Hz).
4.2.7. 3-Bromo-9-butyl-6-phenylethynylcarbazole (6)
Under argon atmosphere, compound 5 (1.13 g, 2.64 mmol) was
dissolved in mixed solvent of dry toluene (10 mL) and (i-Pr)2NH
(8 mL), Pd(PPh3)4 (92.0 mg, 0.08 mmol), CuI (10.0 mg, 0.05 mmol)
were added, then phenylethyne (270.0 mg, 2.64 mmol) was added
via syringe. The mixture was refluxed for 2 h. The reaction mixture
was then cooled to r.t. and the solvent was removed under reduced
pressure. The crude product was purified with column chroma-
tography (silica gel, CH2Cl2:hexane ¼ 1:5, v/v) and a light yellow
oily liquid was obtained, 950.0 mg, yield: 90.0%. 1H NMR (400 MHz,
CDCl3): 8.24 (d, 1H, J ¼ 1.0 Hz), 8.20 (d, 1H, J ¼ 1.7 Hz), 7.67 (q, 1H,
J ¼ 8.5 Hz), 7.59e7.54 (m, 3H), 7.30 (d, 1H, J ¼ 8.8 Hz), 4.29 (t, 2H,
J ¼ 7.3 Hz), 1.88e1.80 (m, 2H), 1.43e1.33 (m, 2H), 0.97 (t, 3H,
J ¼ 7.3 Hz).
4.2.4. Ligand L1
Under argon atmosphere, compound 3 (380.0 mg, 1.54 mmol)
and 4 (360.0 mg, 1.54 mmol) were dissolved in mixed solvent of
toluene (8 mL) and (i-Pr)2NH (8 mL). Then Pd(PPh3)4 (71.9 mg,
0.06 mmol), CuI (24.6 mg, 0.12 mmol) were added, the mixture was
refluxed for ca. 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 CH2Cl2. The organic layer was
dried over anhydrous Na2SO4. After removal of the solvent, the
crude product was purified with column chromatography (silica
gel, CH2Cl2:hexane
¼
1:1, v/v). Orange solid was abstained
(250.0 mg), yield: 40.5%. 1H NMR (400 MHz, CDCl3)： 8.74 (d, 1H,
J ¼ 4.6 Hz), 8.33 (s, 1H), 8.12 (d, 1H, J ¼ 7.9 Hz), 8.05 (d, 2H,
J ¼ 8.1 Hz), 7.82 (t, 2H, J ¼ 7.6 Hz), 7.70e7.65 (m, 3H), 7.52 (t, 1H,
J ¼ 8.0 Hz), 7.44e7.38 (m, 2H), 7.29e7.26 (m, 2H), 4.34 (t, 2H,
J ¼ 7.1 Hz), 1.91e1.84 (m, 2H),1.46e1.37 (m, 2H), 0.98 (t, 3H,
4.2.8. 9-Butyl-3-ethynyl-6-phenylethynylcarbazole (7)
Under argon atmosphere, compound 6 (0.90 g, 2.23 mmol), Pd
(PPh3)4 (104.1 mg, 0.09 mmol), CuI (34.0 mg, 0.18 mmol) were
dissolved in NEt3 (15 mL). After stirring, ethynyltrimethylsilane
(306.8 mg, 3.12 mmol) was added via syringe. The solution was
refluxed for 8 h. The solvent was removed under reduced pressure
and the crude product was purified by column chromatography
(silica gel, dichloromethane/petroleum ether ¼ 1:5, v/v), yellow oil
(600 mg, 1.43 mmol) was obtained, yield: 64.1%. The above trime-
thylsilane protected intermediate was dissolved in methanol
(20 mL), K2CO3 (800 mg,7.55 mmol) was added and the mixture
was stirred at r.t. for 3 h. The solvent was removed under reduced
pressure. Water was added and the mixture was extracted with
CH2Cl2. The organic layer was dried over anhydrous Na2SO4. After
removal of the solvent, compound 3 was obtained. 470.0 mg, yield:
94.8%. 1H NMR (400 MHz, CDCl3): 8.26 (d, 2H, J ¼ 7.0 Hz), 7.66e7.57
(m, 4H), 7.38e7.33 (m, 5H), 4.31 (t, 2H, J ¼ 7.2 Hz), 3.09 (s, 1H),
1.89e1.81 (m, 2H), 1.44e1.34 (m, 2H), 0.97 (t, 3H, J ¼ 7.2 Hz).
J ¼ 7.3 Hz). 13C NMR (100 MHz, CDCl3)
d 156.79, 149.83, 140.96,
140.33, 138.49, 137.08, 132.00, 129.44, 126.94, 126.26, 124.79,
124.28, 123.01, 122.60, 122.45, 120.73, 120.70, 119.51, 113.18, 109.11,
108.94, 92.51, 87.67, 43.15, 31.27, 20.73, 14.06. HRMS
([C29H24N2 þ H]þ) calcd 401.2018, found 401.2020.
4.2.5. Complex Pt-1
Compound L1 (233.0 mg, 0.582 mmol) was dissolved in mixed
solvent of 2-ethoxyethanol (15.0 mL) and water (5 mL), then
K2PtCl4 (120.8 mg, 0.29 mmol) was added, the mixture was heated
to 80 ꢁC for 16 h under argon atmosphere. After cooling to r.t., the
reaction mixture was poured into water (20 mL) and the precipitate
was washed with water (4 ꢂ 20 mL) and dried under vacuum. The

W. Wu et al. / Journal of Organometallic Chemistry 696 (2011) 2388e2398
2397
4.2.9. Ligand L2
4.2.12. Complex Pt-3
Under argon atmosphere, compound 7 (440.0 mg, 1.27 mmol)
and compound 4 (397.3 mg, 1.27 mmol) were dissolved in mixed
solvent of toluene (7 mL) and (i-Pr)2NH (7 mL). Then Pd(PPh3)4
(59.3 mg, 0.05 mmol), CuI (19.3 mg, 0.10 mmol) were added, the
mixture was refluxed for 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 CH2Cl2. The organic
layer was dried over anhydrous Na2SO4. After removal of the
solvent the crude product was purified with column chromatog-
raphy (silica gel, dichloromethane:hexane ¼ 1:1). Orange solid
(274.1 mg, 0.505 mmol) was obtained, yield 40.0%. 1H NMR
(400 MHz, CDCl3): 8.73 (d, 1H, J ¼ 4.8 Hz), 8.30 (d, 2H, J ¼ 5.3 Hz),
8.04 (d, 2H, J ¼ 8.1 Hz), 7.80 (d, 2H, J ¼ 12.3 Hz), 7.70e7.65 (m, 4H),
7.60 (d, 2H, J ¼ 7.2 Hz), 7.39e7.31 (m, 5H), 7.27e7.24 (m, 1H), 4.32 (t,
2H, J ¼ 7.1 Hz), 1.90e1.83 (m, 2H), 1.45e1.36 (m, 2H), 0.98 (t, 3H,
Compound Pt-3 was obtained following a similar procedure
outlined above for Pt-1, except the ligand L3 (100.0 mg,
0.266 mmol) was used instead of L1, yield: 45.0 mg, 50.6%. 1H NMR
(400 MHz, CDCl3)： 9.01 (d, 1H, J ¼ 5.8 Hz), 8.44 (s, 1H), 8.16 (d, 1H,
J ¼ 7.8 Hz), 7.95 (s, 1H), 7.85 (d,1H, J ¼ 8.5 Hz), 7.80 (t,1H, J ¼ 7.8 Hz),
7.64 (d, 1H, J ¼ 8.1 Hz), 7.53 (d, 1H, J ¼ 8.1 Hz), 7.48e7.41 (m, 4H),
7.24 (d,1H, J ¼ 7.3 Hz), 7.10 (t,1H, J ¼ 6.5 Hz), 5.49 (s,1H), 4.35 (t, 2H,
J ¼ 7.0 Hz), 2.03 (s, 3H), 2.02 (s, 3H),1.93e1.85 (m, 2H),1.48e1.38 (m,
2H), 0.98 (t, 3H, J ¼ 7.3 Hz). 13C NMR (100 MHz, CDCl3)
d 185.72,
184.23, 168.24, 147.29, 142.99, 142.94, 140.92, 140.08, 139.07, 138.03,
132.88,129.02,125.64,125.46,123.39,123.23,123.15,122.90,120.77,
120.46, 119.12, 118.79, 118.27, 108.79, 108.73, 102.52, 42.98, 31.19,
29.71, 28.29, 27.28, 20.60, 13.90. MALDI-HRMS ([C32H30N2O4Pt]þ)
calcd 669.1955, found 669.1961.
J ¼ 7.4 Hz). 13C NMR (100 MHz, CDCl3)
d
156.76, 149.74, 140.73,
4.2.13. Oxygen sensing films
140.67, 138.48, 137.22, 137.15, 132.07, 131.69, 129.94, 128.51, 128.02,
127.00, 124.84, 124.42, 124.36, 124.07, 122.73, 122.51, 122.45, 120.81,
120.75, 114.20, 114.13, 114.03, 109.20, 92.31, 90.78, 88.06, 88.03,
43.32, 31.26, 20.68, 13.98. HRMS ([C37H28N2 þ H]þ) calcd 501.2335,
found 501.2331.
Typical film preparation is as following. 10.0 mg of IMPEK-C poly-
mer was dissolved in 0.5 mL chloroform, then 0.4 mL of cyclo-
metalatedplatinumcomplexessolutioninDCM(1.0ꢂ10ꢀ3 moldmꢀ3
)
was added into the solution. After thorough mixing, about 0.25 mL of
the solution was coated on a silica glass disk (diameter: 1.6 cm). The
solvent was evaporated at r.t. and a transparent film was obtained.
The thickness of the film of complex Pt-1 was estimated as 12.7 mm,
by the weight of the film (2.9 mg) and the density of the polymer
(1.14 g cmꢀ3). The thickness of the film of Pt-2 and Pt-3 was estimated
with the same method as 13.2 mm and 11.8 mm, respectively.
4.2.10. Complex Pt-2
Compound Pt-2 was obtained following a similar procedure
outlined above for Pt-1, except the ligand L2 (300.0 mg,
0.599 mmol) was used instead of L1, yield: 15 mg, 6.3%. 1H NMR
(400 MHz, acetone)： 9.15 (s, 1H), 8.95 (d, 1H, J ¼ 5.8 Hz), 8.90 (s,
1H), 8.19e8.12 (m, 3H), 7.70e7.67 (m, 1H), 7.95 (d, 1H, J ¼ 7.7 Hz),
7.80 (d, 1H, J ¼ 8.7 Hz), 7.72e7.65 (m, 3H), 7.37e7.31 (m, 3H), 7.24 (t,
2H, J ¼ 7.3 Hz), 7.17e7.13 (m, 1H), 5.47 (s, 1H), 4.49 (t, 2H, J ¼ 7.0 Hz),
4.42 (s, 2H), 1.92 (s, 3H), 1.86e1.82 (m, 2H), 1.78 (s, 3H), 1.38e1.30
(m, 2H), 0.87 (t, 3H, J ¼ 7.3 Hz). 13C NMR (100 MHz, acetone-d6)
Acknowledgment
We thank the NSFC (20972024 and 21073028), the Fundamental
Research Funds for the Central Universities (DUT10ZD212), Ministry
of Education (SRFDP-200801410004 and NCET-08-0077), the Royal
Society (UK) and NSFC (China-UK Cost-Share Science Networks,
21011130154), PCSIRT (IRT0711), the Education Department of
LiaoningProvince (2009T015), State Key Laboratoryof Fine Chemicals
(KF0802) and Dalian University of Technology for financial support
d
196.53, 196.38, 195.38, 186.31, 184.00, 166.14, 151.35, 147.70,
145.05, 144.15, 140.13, 139.46, 136.10, 132.58, 131.45, 129.87, 129.39,
128.45, 127.84, 127.73, 127.58, 127.50, 127.42, 126.52, 125.89, 125.04,
124.02, 123.74, 123.48, 123.39, 123.07, 122.75, 120.52, 110.60, 110.13,
102.30, 44.87, 43.24, 31.11,27.50, 26.35, 20.23, 13.39. MALDI-MS
([C42H36N2O5Pt]ꢀ) calcd 843.2272, found 843.0262.
Appendix. Supporting information
4.2.11. Ligand L3
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.03.002.
Under Ar atmosphere, compound 4 (400 mg, 1.71 mmol) was
added to anhydrous THF (5.0 mL) in a Schlenk flask at ꢀ78 ꢁC. Then
n-BuLi (2.5 M in hexane, 1.46 ml, 3.42 mmol) was added dropwise.
The mixture was stirred at ꢀ78 ꢁC for 45 min, after which a solution
of anhydrous ZnCl2 (466 mg, 3.42 mmol) in anhydrous THF (10 mL)
was added slowly and the mixture was stirred for 1.5 h at room
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