Cationic iridium(III) complex containing both triarylboron and carbazole moieties as a ratiometric fluoride probe that utilizes a switchable triplet-singlet emission

Article abstract of DOI:10.1002/chem.201000362

A novel cationic Ir^III complex [Ir(Bpq)₂(CzbpyCz)] PF₆ (Bpq = 2-[4-(dimesitylboryl)phenyl]quinoline, CzbpyCz = 5,5′-bis(9-hexyl-9H-carbazol-3-yl) -2,2′ -bipyridine) containing both triarylboron and carbazole moieties was synthesized. The excited-state properties of [Ir(Bpq)₂(CzbpyCz)]PF₆ were investigated through UV/Vis absorption and photoluminescence spectroscopy and molecular-orbital calculations. This complex displayed highly efficient orange-red phosphorescent emission with an emission peak of 583 nm and quantum efficiency of φ = 0.30 in dichloromethane at room temperature. The binding of fluoride ions to [Ir(Bpq)₂(CzbpyCz)]PF₆ can quench the phosphorescent emission from the Ir^III complex and enhance the fluorescent emission from the NN ligand, which corresponds to a visual change in the emission from orange-red to blue. Thus, both colorimetric and ratiometric fluoride sensing can be realized. Interestingly, an unusual intense absorption band in the visible region was observed. And the detection of F^- ions can also be carried out with visible light as the excitation wavelength. More importantly, the linear response of the probe absorbance change at λ= 351 nm versus the concentration of F^- ions allows efficient and accurate quantification of F^- ions in the range 0-50 μM.

Full text of DOI:10.1002/chem.201000362

FULL PAPER
DOI: 10.1002/chem.201000362
Cationic IridiumACTHNUTRGNENGU(III) Complex Containing both Triarylboron and CarbACHTUNGTRENNUNGazole
Moieties as a Ratiometric Fluoride Probe That Utilizes a Switchable
Triplet–Singlet Emission
Wen-Juan Xu,[a] Shu-Juan Liu,[a] Xin-Yan Zhao,[a] Shi Sun,[a] Shan Cheng,[a]
Ting-Chun Ma,[a] Hui-Bin Sun,[a] Qiang Zhao,*[a, b] and Wei Huang*[a]
Abstract: A novel cationic IrIII complex
[Ir(Bpq)2A(CzbpyCz)]PF6 (Bpq=2-[4-
(dimesitylboryl)phenyl]quinoline,
583 nm and quantum efficiency of F=
0.30 in dichloromethane at room tem-
perature. The binding of fluoride ions
blue. Thus, both colorimetric and ratio-
metric fluoride sensing can be realized.
Interestingly, an unusual intense ab-
sorption band in the visible region was
observed. And the detection of Fꢀ ions
can also be carried out with visible
light as the excitation wavelength.
More importantly, the linear response
of the probe absorbance change at l=
351 nm versus the concentration of Fꢀ
ions allows efficient and accurate quan-
tification of Fꢀ ions in the range 0–
50 mm.
N
CHTUNGTRENNUNG
CzbpyCz = 5,5’-bis(9-hexyl-9H-carba-
to [IrACTHGUNTERNNU(G Bpq)2ACHTNUGTREN(NUGN CzbpyCz)]PF6 can quench
zol-3-yl)-2,2’-bipyridine)
containing
the phosphorescent emission from the
IrIII complex and enhance the fluores-
cent emission from the N^N ligand,
which corresponds to a visual change
in the emission from orange-red to
both triarylboron and carbazole moiet-
ies was synthesized. The excited-state
properties of [IrACHTUNGTRENNUNG(Bpq)2ACHTUNGTRENN(UGN CzbpyCz)]PF6
were investigated through UV/Vis ab-
sorption and photoluminescence spec-
troscopy and molecular-orbital calcula-
tions. This complex displayed highly ef-
Keywords:
boron
·
iridium
·
luminescence · phosphorescence ·
sensors
ficient
orange-red
phosphorescent
emission with an emission peak of
Introduction
in a broad range of biological, medical, and chemical pro-
cesses and in applications such as dental care, treatment of
osteoporosis, fluorination of water supplies, and even chemi-
cal and nuclear warfare agents.[1] Consequently, the recogni-
tion and detection of Fꢀ ions are of growing interest and
there is a need to develop new selective and sensitive meth-
ods for the detection of Fꢀ ions in various environments;
therefore, many sensing techniques have been developed for
the purpose of detecting Fꢀ ions. Among these sensing tech-
niques, fluorescent detection is considered to be one of the
most effective tools owing to its high sensitivity, easy visuali-
zation, and short response time for detection. Up until now,
a large number of organic luminophores have been designed
as probes for this important analyte,[2] and most fluorescent
probes are based on variation in the luminescent intensity.
Although these intensity-based probes are of practical utili-
ty, external influences that lead to variations in probe con-
centration and environment can complicate measurements
in practical application. The potential interference can be
minimized by ratiometric detection, which relies on probes
that have two distinct measurable signals in the presence or
absence of the analyte.[2a]
Among the anions, the fluoride ion is attracting particular
interest because it can be considered as both a dangerous
pollutant and useful additive in industrial processes and the
human diet. In addition, fluoride ions play an essential role
[a] W.-J. Xu, Dr. S.-J. Liu, X.-Y. Zhao, S. Sun, S. Cheng, T.-C. Ma,
H.-B. Sun, Dr. Q. Zhao, Prof. W. Huang
Jiangsu Key Laboratory for Organic Electronics & Information
Displays and Institute of Advanced Materials (IAM)
Nanjing University of Posts & Telecommunications (NUPT)
9 Wenyuan Road, Nanjing 210046 (China)
Fax : (+86)25-85866396
E-mail: wei-huang@njupt.edu.cn
iamqzhao@njupt.edu.cn
[b] Dr. Q. Zhao
State Key Laboratory of Coordination Chemistry
Nanjing University
Nanjing, 210093 (China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000362.
Chem. Eur. J. 2010, 16, 7125 – 7133
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7125

The design principles of most fluorescent Fꢀ probes are
based on the formation of a hydrogen bond between the
ꢀ
active N H group of organic luminophores and F ions.[3]
ꢀ
Recently, specific Lewis acid/base interactions, such as the
strong affinity of a boron atom toward Fꢀ ions, have been
adopted as an efficient approach for fluoride detection.[2a–d]
In particular, three-coordinated boron compounds with a di-
mesitylboryl (BMes2) group are highly selective colorimetric
chemosensors for Fꢀ ions.[2a–d,4]
In addition to the widely used organic luminophores, most
recently, phosphorescent heavy-metal complexes have been
applied successfully in the field of chemosensors[5] as a
result of their advantageous photophysical properties, such
as the sensitivity of emission properties to changes in the
local environment, evident Stokes shifts for easy separation
of excitation and emission, significant single-photon excita-
tion in the visible range, and relatively long lifetimes relative
to those of purely organic luminophores. The relatively long
lifetime of these heavy-metal complexes (from the order of
microseconds to milliseconds) can also endow them with a
capacity for excellent temporal resolution, so their lumines-
cence can be easily separated from fluorescent backgrounds
and consequently the signal–noise ratio can be increased. In
addition, relative to purely organic luminophores, the excit-
ed-state properties of phosphorescent heavy-metal com-
plexes are more complicated and depend on the metal
center, chemical structures, and the triplet-state energy
levels of the ligands. If the ligand of a heavy-metal complex
contains a specific coordinating element for an analyte, the
presence of this analyte can lead to dramatic variation in
the photophysical and electrochemical properties of the
complex, thus realizing detection. According to this princi-
ple, we have successfully realized excellent phosphorescent
probes for Hg2+ ions, anions, and homocysteine.[6] In addi-
tion, the introduction of BMes2 groups into the ligand of
phosphorescent heavy-metal complexes can also realize
novel phosphorescent Fꢀ probes through the specific inter-
action of the boron atom with Fꢀ ions, which can induce var-
iations in the excited-state properties of heavy-metal com-
plexes.[6c,7]
As a class of novel phosphorescent material, there have
been several investigations into phosphorescent CuI, PtII,
ReI, RuII, and IrIII complexes containing BMes2 groups by us
and others over the past three years.[6c,7] Most of these re-
ports are based on the principle of incorporating BMes2
groups into the conjugated structure of the ligand and that
binding with Fꢀ ions induces variation in the phosphorescent
signal. Most recently, Wang and co-workers observed an in-
teresting ambient-temperature singlet–triplet dual emission
for nonconjugated donor–acceptor triarylboron–PtII com-
plexes (see Figure 1a).[7g] Furthermore, binding of Fꢀ ions
can increase both the singlet and triplet emissions, and the
enhanced degree of triplet emission is higher than that of
the singlet emission. Therefore, how to design ratiometric
probes with a switchable triplet–singlet emission is very in-
teresting. However, up until now, there have been no re-
ports on the realization of such ratiometric probes that uti-
Figure 1. Phosphorescent Fꢀ probes based on heavy-metal complexes
containing the BMes2 group with nonconjugated (a) and conjugated (b)
structures utilizing triplet–singlet dual emissions.
lize a triplet–singlet emission switch for phosphorescent
heavy-metal complexes containing BMes2 groups in the con-
jugated structure of the ligand (Figure 1b).
Herein, we have designed and synthesized the novel cat-
ionic IrIII complex [Ir
ACHTNUGTRNNEUG(Bpq)2ACHTUNGTNER(NUGN CzbpyCz)]PF6 (Bpq=2-[4-(di-
mesitylboryl)phenyl]quinoline, CzbpyCz= 5,5’-bis(9-hexyl-
9H-carbazol-3-yl)-2,2’-bipyridine; Scheme 1) with dimesityl-
boryl groups on the cyclometalated C^N ligands (Bpq). The
2,2-bipyridine-based oligomer CzbpyCz with carbazole units
was selected as an N^N ligand that can act as energy donor.
Different from the work of Wang and co-workers, the
energy donor and acceptor were incorporated into the com-
plex through a conjugated binding approach. The ratiomet-
ric and colorimetric detection of Fꢀ ions was realized by
switchable fluorescence and phosphorescence from the N^N
ligand and complex, respectively. Interestingly, an unusual
intense absorption band in the visible region was observed.
Therefore, the detection of Fꢀ ions can also be carried out
with visible light as the excitation wavelength.
Results and Discussion
Synthesis and characterization of [Ir
Scheme 1 shows the synthetic route to the target IrIII com-
plex [Ir(Bpq)2A(CzbpyCz)]PF6. The N^N ligand CzbpyCz was
ACHUTGTNERN(NGU Bpq)2ACHUTNGTREN(NNGU CzbpyCz)]PF6:
A
CHTUNGTRENNUNG
synthesized from 9-hexyl-9H-carbazol-3-ylboronic acid and
5,5’-dibromo-2,2’-bipyridine by using the Suzuki–Miyaura
cross-coupling reaction.[8] The synthesis of the cyclometalat-
ed C^N ligand Bpq comprises two steps: First, precursor 2-
(4-bromophenyl)quinoline (Brpq) was easily obtained in
good yield by a Friedlꢁnder condensation reaction of 2-ami-
nobenzadehyde with 4-bromoacetophenone according to a
previously reported procedure.[9] Second, ligand Bpq was
synthesized in 60% yield by lithiating Brpq, followed by the
addition of dimesitylboron fluoride (Mes2BF) at ꢀ788C.[10]
The dinuclear cyclometalated IrIII chloro-bridged precursor
[{IrACTHNURTGNE(NUG Bpq)2Cl}2] with Bpq as a cyclometalated ligand was syn-
thesized by using the same method as Nonoyama.[11] The
cationic IrIII complex was routinely synthesized in high
yields of 70% by treating the cyclometalated IrIII chloro-
bridged precursor with the CzbpyCz ligand. The structure of
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Cationic IrIII Complex as a Luminescent Fluoride Probe
FULL PAPER
Scheme 1. The synthetic route to [IrACHTUNRGTENNUG(Bpq)2ACHTUNGTREN(NGUN CzbpyCz)]PF6. TBABr=tetrabutylammonium bromide.
1
the target complex was characterized by H and 13C NMR
spectroscopic and MALDI-TOF mass spectrometry.
Photophysical properties of the N^N ligand CzbpyCz: The
UV/Vis absorption and photoluminescent (PL) spectra of
the CzbpyCz ligand are shown in Figure 2 and the data are
summarized in Table 1, which are also compared with bipyr-
idine. Relative to bipyridine, CzbpyCz showed redshifted
and intense absorption bands centered at l=245, 300, and
353 nm with molar extinction coefficients of e>
104 molꢀ1 dm3 cmꢀ1. The absorption bands centered at l=
245 and 300 nm of CzbpyCz can be assigned to p–p* transi-
tions from the bipyridine and carbazole units. To clarify the
origin of the intense absorption band at l=353 nm, molecu-
lar-orbital calculations for CzbpyCz were performed by
using time-dependent density functional theory (TDDFT)
calculations (see Figure 3). Ac-
Figure 2. UV/Vis absorption spectra of bipyridine and CzbpyCz moieties,
and the PL spectra of CzbpyCz under different conditions at room tem-
perature.
cording to the calculation re-
Table 1. Photophysical data for CzbpyCz and [IrACTHNGURTEN(NUGN Bpq)2ACHTUNGTRENNUNG
(CzbpyCz)]PF6 at 298 K.
lem [nm]
(CH2Cl2)
sults, the HOMO is mainly lo-
calized at the carbazole moiet-
ies with some contribution from
the bipyridine unit, and the
LUMO is localized at the bipyr-
idine moiety. The absorption of
CzbpyCz at l=353 nm is
Compound
labs [nm]
(loge)
lem [nm]
ACHTUNGTNER(NUGN CH3CN)
F[a]
t [ms]
U
G
Bpy
CzbpyCz
235
245
268
N
ACHTUNGTRENNUNG
A
G
436
583
450
584
0.83
0.30
[Ir
N
(CzbpyCz)]PF6
A
G
(4.62)
1.96
[a] The quantum efficiency for CzbpyCz was obtained under air with 9,10-diphenylanthracene as an external
standard; the quantum efficiency for [IrCATHUNGTRNE(NNGU Bpq)2ACHTUNRTGEG(NNUN CzbpyCz)]PF6 was measured under N2 with [IrACHTNUGERTN(NUGN ppy)3] as an ex-
mainly
attributed
to
a
ternal standard (F=0.40).[12]
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Q. Zhao, W Huang et al.
Complex
[IrACHTUNGTRENNUNG(Bpq)2-
AHCTUNTGREN(NGNU CzbpyCz)]PF6 showed an in-
tense emission band at about
l=583 nm with an orange-red
emission at room temperature
in CH2Cl2, which had little de-
pendence on the solvent polari-
ty and temperature (Figure 4).
Figure 3. HOMO and LUMO orbitals of CzbpyCz.
According to previous studies
on cationic IrIII complexes con-
HOMO!LUMO excitation. Therefore, the lowest electron-
ic transition of CzbpyCz can be mainly assigned to a charge-
transfer (CT) state from the carbazole to bipyridine units
with a p–p* transition of the bipyridine moiety.
taining diimine ligands, their excited states are very compli-
cated and the emission often comes from mixed excited
states containing 3LC, 3MLCT, and 3LLCT transitions.[13]
The emissions from ligand-centred 3LC
ACTHNUTRGNEUNG(p–p*) states often
It can be seen that CzbpyCz displayed an intense-blue
emission in CH2Cl2 with a maximal emission wavelength at
l=436 nm and a quantum efficiency of F=0.83 (Figure 2).
In addition, the emission spectrum of CzbpyCz has a de-
pendence on the solvent polarity as the lmax value shifts to
l=450 nm in CH3CN, thus indicating the CT character of
the excited state, which is in accordance with the TDDFT
calculation results.
Photophysical properties of [Ir
UV/Vis absorption and PL spectra of [Ir
(CzbpyCz)]PF6 are shown in Figure 4 and the data are sum-
ACHUTGTERNN(UG Bpq)2ACHTUNGTR(EUNNNG CzbpyCz)]PF6: The
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
marized in Table 1. The complex displayed intense absorp-
tion bands at l=250–400 nm, related to the singlet ligand-
centered p–p* transitions from the Bpq and CzbpyCz li-
gands. Interestingly, the complex showed an unusual intense
absorption band at l=430 nm with e>104 molꢀ1 dm3 cmꢀ1.
As confirmed by TDDFT calculations (see Figure 5 and
Table 2), this intense absorption
Figure 4. UV/Vis absorption spectra and the normalized emission spectra
of [Ir(Bpq)2A(CzbpyCz)]PF6 under different conditions.
N
CHTUNGTRENNUNG
at l=430 nm mainly originates
from the S4 state, namely,
HOMO!LUMO
and
HOMOꢀ1!LUMO transitions,
thus corresponding to CT char-
acter from the HOMO and
HOMOꢀ1 that reside on the
carbazole fragment to the
LUMO localized on the bipy-
drine fragment, which is similar
to the CT transition of the free
CzbpyCz ligand in l=353 nm,
except that the lmax value of
this band in the complex is red-
shifted. In addition, the weak
absorption bands of the com-
plex in the region l=450–
550 nm can be assigned to a
mixture of ligand-to-ligand
charge-transfer (LLCT), metal-
to-ligand
charge-transfer
(MLCT), and ligand-centred
(LC) transitions.
Figure 5. HOMO, HOMOꢀ1, HOMOꢀ8, and LUMO orbitals of [Ir
ACHUTGTNERN(NGU Bpq)2ACHUTNGTREN(NNGU CzbpyCz)]PF6.
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Cationic IrIII Complex as a Luminescent Fluoride Probe
FULL PAPER
Table 2. Calculated energy levels of the lowest singlet and triplet states
for [Ir
ACHTUNGTRENNUNG(Bpq)2ACHTUNGTRENNUNG(CzbpyCz)]PF6.
[a]
[a]
State Excitation
Ecalcd
lcalcd
f[b]
[eV]
[nm]
531
HOMOꢀ1!LUMO (46%)
S1
S2
S3
S4
T1
2.33
2.49
2.50
2.62
2.19
0.0123
0.0022
0.0420
0.68
HOMO!LUMO (52%)
HOMOꢀ1!LUMO+1 (46%)
HOMO!LUMO+1 (51%)
HOMOꢀ1!LUMO+2 (46%)
HOMO!LUMO+2 (50%)
HOMOꢀ1!LUMO (52%)
HOMO!LUMO (45%)
497
495
473
567
HOMOꢀ8!LUMO (20%)
HOMO!LUMO (64%)
0
[a] Ecalcd: calculated energy. [b] f: calculated oscillator strength.
display vibronic progressions and small dependence on sol-
vent polarity and temperature, whereas those emissions
from CT states are often broad, featureless, and sensitive to
solvent polarity and temperature.[13,14] No vibronic progres-
sions were observed, thus indicating that the excited state of
the complex has some CT character. In addition, the PL
Figure 6. Change in the UV/Vis absorption spectra of [Ir
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG(Bpq)2-
spectra of [IrACHTUNGTRENNUNG(Bpq)2ACHTUNGTRENNUNG(CzbpyCz)]PF6 are insensitive to solvent
3
polarity and temperature, thus indicating that the LC tran-
sition dominates in the excited states. The phosphorescence
quantum yield in degassed CH2Cl2 is F=0.30, and the emis-
sion lifetime at l=583 nm is t=1.96 ms, thus indicating the
phosphorescent nature of the emission.
Molecular orbital calculations for [Ir
were performed by using TDDFT calculations (Figure 5 and
Table 2). The lowest triplet state (T1) of [Ir(Bpq)2-
(CzbpyCz)]PF6 originates from HOMO!LUMO and
ACHUTNGTNERNUG(Bpq)2CAHTUNGTRENN(NGU CzbpyCz)]PF6
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
HOMOꢀ8!LUMO transitions. The HOMO distribution
primarily resides on the carbazole fragments with some lo-
calized on the phenyl rings of the cyclometalated ligands
and the IrIII center, and the HOMOꢀ8 distribution primarily
resides on the CzbpyCz ligand. The LUMO distribution is
dominated by the bipyridine fragment. Hence, the lowest
triplet state apparently possesses more ligand-centred (N^N
ligand) character (3LC) and mixes with some pphenyl!p*N^N
(3LLCT) and dp(Ir center)!p*N^N (3MLCT) transitions, which
is in accordance with the emission character.
Optical responses of [Ir
N
(CzbpyCz)]PF6 to Fꢀ ions:
2ACHTUNGTRENNUNG
The response of [Ir(Bpq) CHTUTGNRENNUNG
G
vestigated through UV/Vis absorption and emission spectro-
scopic analysis. Figure 6 shows the variation in the absorp-
tion spectra of [IrACHTUNGTRENNUNG(Bpq)2CAHTUNGTRNEN(UGN CzbpyCz)]PF6 upon the addition of
Fꢀ ions. The absorptions at l=291 and 351 nm decreased
gradually, whereas the absorption at l=414 nm increased
gradually, which corresponds to an isobestic point at l=
379 nm. Additionally, the absorbance at l=430–550 nm de-
creased gradually, thus corresponding to another isobestic
point at l=430 nm.
Figure 7. a) Change in the emission spectra of [Ir
(20 mm) in CH3CN with various amounts of Fꢀ ions excited at l=379 nm.
Inset: color of the emission observed of [IrCAHTGNURTEN(NUNG Bpq)2ACHUTNGRENUN(G CzbpyCz)]PF6 in
ACHUTNGTNERNUG(Bpq)2CAHTUNGTRENN(NGU CzbpyCz)]PF6
CH3CN (20 mm) in the absence (left) and presence (right) of Fꢀ ions.
b) Fluorescent titration profile of I584/I458 versus the equivalents of Fꢀ
ions added.
The variation in the PL spectra with l=379 nm as the ex-
citation wavelength is shown in Figure 7a. Upon the addi-
decreased gradually and was blueshifted to l=572 nm,
whereas the emission intensity at l=458 nm, which is tenta-
tively attributed to the emission of the CzbpyCz ligand, in-
tion of Fꢀ ions to a solution of [Ir
G
2ACHTUNGTREN(NUNG CzbpyCz)]PF6 in
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7129

Q. Zhao, W Huang et al.
creased gradually with a clear isoemission point at l=
540 nm, thus realizing ratiometric Fꢀ sensing. The ratios of
emission intensities at l=584 and 458 nm (I584/I458) exhibit a
dramatic change from 24.0:1 to 0.4:1. Such a large change of
emission intensity ratios at two wavelengths is desirable for
ratiometric fluorescent probes, as the sensitivity and the dy-
namic range of ratiometric probes are controlled by the
emission ratio. Furthermore, the difference in the two emis-
sion wavelength is very large (l=126 nm). This difference
not only contributes to the accurate measurement of two
emission intensities, but also results in a huge ratiometric
value. More interestingly, an obvious change of emission
color from orange/red to blue was observed (Figure 7a,
inset), thus enabling colorimetric Fꢀ sensing. The short emis-
sion lifetime (t=5.71 and 1.18 ns) of the new blue emission
at l=458 nm indicates the fluorescent nature of the com-
plex. Furthermore, the emission wavelength and band shape
of the blue emission are similar to those of the N^N ligand
CzbpyCz, thus indicating that the blue emission at l=
458 nm originates from the singlet emission of CzbpyCz.
Figure 8. Change in the emission spectra of [IrACHTNUTRGENNUG(Bpq)2ACHTUNGTRENN(UGN CzbpyCz)]PF6
(20 mm) in CH3CN with various amounts of Fꢀ ions excited at l=430 nm.
That is to say, binding of Fꢀ ions to [Ir
A
N
The calibration factor f is defined to minimize the influence
of the absorption background in the absence of Fꢀ ions.
Figure 9 shows f as a function of the concentration of Fꢀ
quenched the triplet emission from the IrIII complex and
switched on the singlet emission from the N^N ligand.
After the addition of approximately two equivalents of Fꢀ
ions, the emission intensity ratio of I584/I458 reaches satura-
tion point (see the emission titration curves in Figure 7b).
Considering that there are two boron centers in one mole-
ions in CH3CN. Complex [IrACTHNUGTRENNUG(Bpq)2AHCUTGNTREN(NUGN CzbpyCz)]PF6 gives a
cule of the complex, it is possible for [Ir
ACHTUNGERTN(NUNG Bpq)2-
ACHTUNGTRENNUNG(CzbpyCz)]PF6 to form a 1:2 complex with two equivalents
of Fꢀ ions because the two dimesitylboryl groups are elec-
tronically separated in the ground state and spatially distant
from each other. Using the UV/Vis titration data, the bind-
ing constants (K1 and K2) of the IrIII complex were deter-
mined to be 6.60ꢂ105 and 2.04ꢂ103 mꢀ1, respectively, which
are similar to the values reported previously for boryl-based
fluorescent and phosphorescent receptors.[2d,6c]
One of the challenges in the design of luminescent che-
mosensors, particularly those aimed at bioanalysis and prac-
tical application, is to shift the excitation wavelength from
the UV region to the visible range because a lot of back-
ground fluorescence can not be excited by visible light and
visible excitation requires cheaper optical cells and optics.
Figure 9. A plot of f as a function of the concentration of Fꢀ ions for [Ir-
(Bpq)2A(CzbpyCz)]PF6 (20 mm) in CH3CN at room temperature.
N
CHTUNGTRENNUNG
In view of the strong absorption of [Ir
within the visible region, the variation in the PL spectra of
[Ir(Bpq)2A
(CzbpyCz)]PF6 responsive to Fꢀ ions excited at l=
430 nm was investigated. The orange-red emission at l=
2A
was blueshifted to l=572 nm on the addition of Fꢀ ions,
whereas the blue emission at l=458 nm was not observed,
thus indicating that the detection excited by visible light was
also realized (Figure 8).
ACHUTNGTNERNUG(Bpq)2CAHTUNGTRENN(NGU CzbpyCz)]PF6
linear response for Fꢀ ions at 0–50 mm and the correlation
coefficient is 0.99, which is suitable for monitoring Fꢀ ions
and quantification at 0–50 mm (Figure 9).
G
CHTUNGTRENNUNG
584 nm of [IrACHTUNGTRENNUNG(Bpq) CHTUNGTRENNUNG(CzbpyCz)]PF6 decreased gradually and
Sensing mechanism of [Ir
orbital calculations for
(CzbpyCz)]PF6·2Fꢀ were performed by using TDDFT calcu-
lations to better understand the sensing mechanism of [Ir-
(Bpq)2A(CzbpyCz)]PF6 (see Figure 10 and Scheme 2). For the
A
U
the
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
CHTUNGTRENNUNG
Quantification of Fꢀ ions: To quantify the concentration of
Fꢀ ions in solution, the change in the absorption spectra is
correlated to the analyte concentration by using f=(A0ꢀA)/
A0, where A and A0 are the absorbances at l=351 nm in
the presence and absence of Fꢀ ions, respectively (Figure 6).
adduct, the lowest triplet state originates from HOMOꢀ2!
LUMO (50%) and HOMOꢀ4!LUMO (36%) transitions.
The HOMOꢀ2 and HOMOꢀ4 distributions primarily
ꢀ
ꢀ
reside on the BMes2 F fragments, and the LUMO distribu-
tion resides on the bipyridine fragment. Therefore, the T1 of
7130
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Chem. Eur. J. 2010, 16, 7125 – 7133

Cationic IrIII Complex as a Luminescent Fluoride Probe
FULL PAPER
Hence, we can see that there
is energy transfer from the
CzbpyCz ligand to the IrIII com-
plex from the spectra proper-
ties, the emission-titration ex-
periment, and theoretical calcu-
lation results. Before binding
with Fꢀ ions, the energy trans-
fer is efficient and only the trip-
let-state emission of the com-
plex is observed (Scheme 2).
However, binding with Fꢀ ions
can inhibit the energy transfer,
and the singlet emission from
CzbpyCz is restored. Hence,
the triplet–singlet dual emission
can be switched through bind-
ing of Fꢀ ions.
Figure 10. HOMOꢀ2, HOMOꢀ4, and LUMO orbitals of [Ir
(CzbpyCz)]PF6·2Fꢀ.
ACHUTGTNRNENUG(Bpq)2ACHTUNGTRENNUGN
Selectivity towards Fꢀ ions:
High selectivity is necessary for
an excellent chemosensor. Ach-
ieving high selectivity for the
analyte of interest over a com-
plex background of potentially
competing species is, however,
a challenge in sensor develop-
ment. Herein, the selective co-
ordination studies of the com-
plex
[IrACTHUNGRTENNU(G Bpq)2ACHTUNGTRENUN(NG CzbpyCz)]PF6
were extended to other anions
in CH3CN. Only the addition of
Fꢀ ions results in prominent
changes of luminescence inten-
sity at l=584 nm, whereas the
addition of an excess of other
(CzbpyCz)]PF6 to Fꢀ ions.
Scheme 2. The sensing mechanism of [IrACTHNUTRGENNUG(Bpq)2ACHTUNGTRENNUGN
3
ꢀ
ꢀ
ꢀ
[Ir
(Bpq)
N
anions (Clꢀ, Brꢀ, Iꢀ, ClO4 , NO3 , H2PO4 , and CH3COOꢀ)
causes little or slight changes (Figure 11). Therefore, the
complex displayed a high selectivity in sensing Fꢀ ions.
transition from the BMes2 group to the N^N ligand. We ten-
tatively think that this transition is responsible for the emis-
sion at l=572 nm of [IrACHTUNGRTENNUG(Bpq)2ACHTUNTGREN(NUNG CzbpyCz)]PF6 after binding
with Fꢀ ions.
The PL spectra of the CzbpyCz ligand, [Ir
(CzbpyCz)]PF6, and the adduct [Ir(Bpq)2A
(CzbpyCz)]PF6·2Fꢀ
and the absorption spectrum of [Ir(Bpq)2A(CzbpyCz)]PF6 are
ACHTUNGERTN(NUNG Bpq)2-
A
R
CHTUNGTRENNUNG
A
CHTUNGTRENNUNG
shown in Figure S4 in the Supporting Information. There is
a good spectral overlap between the PL emission spectrum
of the free CzbpyCz ligand and the absorption spectrum of
[IrACHTUNGTRENNUNG(Bpq)2ACHTUNGTRENNUNG(CzbpyCz)]PF6, which maybe ensures an efficient
Fçrster energy transfer from the CzbpyCz ligand to the Ir
complex. In addition, before binding with Fꢀ ions, the PL
emission spectrum of the complex mainly showed a triplet
emission from the IrIII complex. Whereas the PL emission
(CzbpyCz)]PF6·2Fꢀ showed
spectrum of the adduct [IrACHTNUGRTNENUG(Bpq)2ACHTUNGTRENNUGN
Figure 11. Emission response of [IrACHTUNRGTENNUG(Bpq)2ACHTUNTGREN(NUGN CzbpyCz)]PF6 (20 mm) in the
a strong singlet emission from the CzbpyCz ligand and a
weak emission at l=572 nm. Hence, we can think that the
energy transfer becomes inefficient after binding with Fꢀ
ions.
presence of various anions (4 equiv) in CH3CN. Bars represent the emis-
sion intensity at l=584 nm. Gray and white represent I584 nm before and
after the addition of anions, respectively. 1) Fꢀ, 2) Clꢀ, 3) Brꢀ, 4) Iꢀ,
5) NO3ꢀ, 6) ClO4ꢀ, 7) H2PO4ꢀ, 8) CH3COOꢀ.
Chem. Eur. J. 2010, 16, 7125 – 7133
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7131

Q. Zhao, W Huang et al.
with ethyl acetate/petroleum ether (1:3) as the eluent to yield a yellow
solid. Recrystallization from CH2Cl2/hexane gave yellow crystals in 60%
yield. 1H NMR (400 MHz, CDCl3): d=9.08 (d, J=2.03 Hz, 2H; ArH),
8.56 (d, J=8.22 Hz, 2H; ArH), 8.40 (d, J=1.43 Hz, 2H; ArH), 8.15–8.20
(m, 4H; ArH) 7.81–7.78 (m, 2H; ArH), 7.55–7.44 (m, 6H; ArH), 7.31 (t,
Conclusion
We have synthesized the novel cationic IrIII complex [Ir-
ACHTUNGTRENNUNG(Bpq)2ACHTUNGTRENNUNG(CzbpyCz)]PF6, containing dimesitylboryl and carba-
ꢀ
zole groups, that has an intense absorption at l=430 nm
with molar extinction coefficients of e>104 molꢀ1 dm3 cmꢀ1
and displayed highly efficient orange/red phosphorescent
emission at l=584 nm at room temperature. This IrIII com-
plex can be used as a highly selective phosphorescent probe
J=7.47 Hz, 2H; ArH), 4.35 (t, J=7.20 Hz, 4H; N CH2), 1.95–1.88 (m,
4H; CH2), 1.46–1.26 (m, 12H; CH2), 0.88 ppm (t, J=7.20 Hz, 6H; CH3);
13C NMR (100 MHz, CDCl3): d=154.20, 147.98, 141.14, 140.58, 137.46,
135.35, 128.63, 126.30, 125.06, 123.80, 123.00, 121.10, 120.76, 119.38,
119.11, 109.53, 109.19, 43.48, 31.82, 29.21, 27.22, 22.79, 14.28 ppm.
[IrACHTUGNTERN(NUNG Bpq)2ACHTUNGTRENGU(N CzbpyCz)]PF6: [IrAHCTUNGERTNGUN(N Bpq)2ACHTNGUTNER(NUGN CzbpyCz)]PF6 was synthesized
for Fꢀ ions. Binding of Fꢀ ions to [Ir
ACHTNUTRGNNEUG(Bpq)2CAHTUNGTRENN(NGU CzbpyCz)]PF6
through a standard two-step procedure according a reported method.[6c]
A mixture of 2-ethoxyethanol and water (3:1, v/v) was added to a flask
containing IrCl3·3H2O (1 mmol) and Bpq (2.5 mmol). The reaction mix-
ture was heated to reflux for 24 h. After cooling, an orange solid precipi-
tate was removed by filtration to give the crude cyclometalated IrIII
quenched the phosphorescent emission from the IrIII com-
plex and switched on the fluorescent emission from the
N^N ligand, which corresponds to a visual change in the
emission color from orange-red to blue, thus enabling colori-
metric as well as ratiometric fluoride ion sensing. Further-
more, phosphorescent detection of Fꢀ ions excited with visi-
ble light was also realized. More importantly, the linear re-
sponse of the change in the probe absorbance at l=351 nm
versus the concentration of Fꢀ ions allows efficient and ac-
curate Fꢀ quantification in the range 0–50 mm. We think that
this result will be very useful for the further design of excel-
lent phosphorescent ratiometric probes that utilize switcha-
ble triplet and singlet emissions.
chloro-bridged dimer.
A
solution of the cyclometalated IrIII chloro-
bridged dimer (0.079 mmol) and CzbpyCz (0.158 mmol) in CH2Cl2/
MeOH (30 mL, 2:1 v/v) was heated to reflux. The red solution was
cooled to room temperature after 4 h and a 10-fold excess of potassium
hexafluorophosphate was added. The suspension was stirred for 2 h, fil-
tered to remove any insoluble inorganic salts, and evaporated to dryness
under reduced pressure. The crude product was purified with column
chromatography on silica gel with CH2Cl2/acetone (50:1) as the eluent to
afford an orange/yellow solid in 60% yield. 1H NMR (400 MHz, CDCl3):
d=8.58–8.30 (m, 6H; ArH), 8.08–7.91 (m, 10H; ArH), 7.56–7.35 (m,
18H; ArH), 7.02 (s, 3H; ArH), 6.54–6.41 (m, 9H; ArH), 4.35 (t, J=
6.85 Hz, 4H; N-CH2), 2.24 (s, 12H; CH3), 1.93–1.86 (m, 4H; CH2), 1.67
(s, 24H; CH3), 1.39–1.19 (m, 12H; CH2), 0.88 ppm (t, J=6.91 Hz, 6H;
CH3); 13C NMR (100 MHz, CDCl3): d=131.48, 130.36, 128.99, 127.97,
127.85, 127.05, 126.81, 125.44, 125.12, 124.99, 124.81, 124.19, 124.00,
122.76, 120.77, 119.98, 118.47, 117.26, 110.02, 109.46, 43.56, 31.80, 29.19,
27.19, 23.16, 22.79, 21.51, 14.28 ppm; MS (MALDI-TOF) (m/z): 1753.0
[MꢀPF6]+.
Experimental Section
Characterization: NMR spectra were recorded on a Bruker Ultra Shield
Plus 400 MHz NMR instrument (1H: 400, 13C: 100 MHz). The mass spec-
tra were obtained on a Bruker autoflex MALDI-TOF/TOF mass spec-
trometer. The UV/Vis absorption spectra were recorded on a Shimadzu
UV-3600 UV/Vis-NIR spectrophotometer. The PL spectra were mea-
sured using a RF-5301PC spectrofluorophotometer. The quantum effi-
ciency for CzbpyCz was obtained under air using 9,10-diphenylanthra-
Acknowledgements
cene as an external standard. The quantum efficiency for [Ir
(CzbpyCz)]PF6 was measured in degassed CH2Cl2 with fac-[Ir
(ppy=2-phenylpyridine) as an external standard (F=0.40).
ACHTUNGTRENNUNG
This work was financially supported by the National Basic Research Pro-
gram of China (973 Program, 2009CB930601), National Natural Science
Foundation of China (project no. 50803028, 20804019, and 20774043),
Natural Science Foundation of Jiangsu Province of China (BK2009427),
Natural Science Fund for Colleges and Universities in Jiangsu Province
(08 KJD430017), Scientific and Technological Innovation Teams of Col-
leges and Universities in Jiangsu Province (TJ207035 and TJ209035),
Nanjing University of Posts and Telecommunications (project no.
NY208045), and the Program for Postgraduates Research Innovations in
University of Jiangsu Province (CX08B_084Z).
G
ACHTUNGTRENNUNG
Theoretical calculations: The calculation was performed using the Gaus-
sian 03 suite of programs.[15] The optimizations of the ligand and complex
structures were performed by using B3LYP DFT. The LANL2DZ basis
set was used to treat the iridium atom, whereas the 6–31G* basis set was
used to treat all other atoms. The contours of the HOMOs and LUMOs
were plotted.
Materials: All reagents, unless specified, were obtained from Sigma–Al-
drich, Acros, and Alfa and were used as received. All solvents were puri-
fied before use. All the reactions were performed in a nitrogen atmos-
phere.
[1] a) K. L. Kirk, Biochemistry of the Halogens and Inorganic Halides,
Plenum Press, New York 1991, p. 58; b) B. L. Riggs, Bone and Min-
eral Research, Elsevier, Amsterdam, 1984, p. 366; c) A. Wiseman,
Handbook of Experimental Pharmacology XX/2, Part 2, Springer,
Berlin 1970, p. 48; d) P. Connet, Fluoride 2007, 40, 155–158;
e) R. G. Foulkes, Fluoride 2007, 40, 229–237; f) S. Ayoob, A. K.
Gupta, Crit. Rev. Environ. Sci. Technol. 2006, 36, 433–487; g) E. B.
Bassin, D. Wypij, R. B. Davis, Cancer Causes Control 2006, 17, 421–
428; h) Y. Yu, W. Yang, Z. Dong, C. Wan, J. Zhang, J. Liu, K. Xiao,
Y. Huang, B. Lu, Fluoride 2008, 41, 134–138.
[2] a) Y. Kubo, M. Yamamoto, M. Ikeda, M. Takeuchi, S. Shinkai, S. Ya-
maguchi, K. Tamao, Angew. Chem. 2003, 115, 2082–2086; Angew.
Chem. Int. Ed. 2003, 42, 2036–2040; b) Z. Q. Liu, M. Shi, F. Y. Li,
Q. Fang, Z. H. Chen, T. Yi, C. H. Huang, Org. Lett. 2005, 7, 5481–
5484; c) M. H. Lee, T. Agou, J. Kobayashi, T. Kawashima, F. P.
Gabbaꢃ, Chem. Commun. 2007, 1133–1135; d) X. Y. Liu, D. R. Bai,
S. Wang, Angew. Chem. 2006, 118, 5601–5604; Angew. Chem. Int.
Synthesis
9-Hexylcarbazol-3-boronic acid: This compound was synthesized by using
a reported procedure in a yield of 50%.[16]
2-(4-Bromophenyl)quinoline (Brpq): This compound was synthesized by
using a reported procedure in a yield of 75%.[9]
2-[4-(Dimesitylboryl)phenyl]quinoline (Bpq): This compound was syn-
thesized by using a reported procedure in a yield of 60%.[10]
CzbpyCz: A degassed mixture of toluene ([monomer]=0.25m), aqueous
potassium carbonate (2m), and ethanol (2:1:1 v/v/v) was added to a mix-
ture of 5,5’-dibromo-2,2’-bipyridine (0.16 g, 0.5 mmol), 9-hexylcarbazol-3-
boronic acid (0.31 g, 1.05 mmol), and [PdACTHNUTRGNEUNG(PPh3)4] (0.003 g, 0.0025 mmol).
The reaction mixture was vigorously stirred at 708C for 12 h. The reac-
tion mixture was cooled to room temperature, washed with brine, extract-
ed with CH2Cl2 (3ꢂ), dried over anhydrous Na2SO4, and concentrated.
The crude product was purified by column chromatography on silica gel
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Cationic IrIII Complex as a Luminescent Fluoride Probe
FULL PAPER
Ed. 2006, 45, 5475–5478; e) K. Parab, K. Venkatasubbaiah, F. Jꢁkle,
J. Am. Chem. Soc. 2006, 128, 12879–12885; f) S. Yamaguchi, S.
Akiyama, K. Tamao, J. Am. Chem. Soc. 2001, 123, 11372–11375.
[3] a) P. D. Beer, P. A. Gale, Angew. Chem. 2001, 113, 502–532; Angew.
Chem. Int. Ed. 2001, 40, 486–516; b) H. Miyaji, W. Sato, J. L. Sess-
ler, Angew. Chem. 2000, 112, 1847–1850; Angew. Chem. Int. Ed.
2000, 39, 1777–1780; c) C. B. Black, B. Andrioletti, A. C. Try, C.
Ruiperez, J. L. Sessler, J. Am. Chem. Soc. 1999, 121, 10438–10439;
d) E. J. Cho, J. W. Moon, S. W. Ko, J. Y. Lee, S. K. Kim, J. Yoon,
K. C. Nam, J. Am. Chem. Soc. 2003, 125, 12376–12377; e) M. Boioc-
chi, L. Del Boca, D. E. Gomez, L. Fabbrizzi, M. Licchelli, E. Monza-
ni, J. Am. Chem. Soc. 2004, 126, 16507–16514; f) K. Chellappan,
N. J. Singh, I. C. Hwang, J. W. Lee, K. S. Kim, Angew. Chem. 2005,
117, 2959–2963; Angew. Chem. Int. Ed. 2005, 44, 2899–2903.
[4] a) T. Agou, J. Kobayashi, T. Kawashima, Inorg. Chem. 2006, 45,
9137–9144; b) C. D. Entwistle, T. B. Marder, Angew. Chem. 2002,
114, 3051–3056; Angew. Chem. Int. Ed. 2002, 41, 2927–2931; c) M.
Melaimi, F. P. Gabbaꢃ, J. Am. Chem. Soc. 2005, 127, 9680–9681;
d) T. W. Hudnall, F. P. Gabbaꢃ, J. Am. Chem. Soc. 2007, 129, 11978–
11986.
[5] a) P. Anzenbacher, Jr., D. S. Tyson, K. Jursikova, F. N. Castellano, J.
Am. Chem. Soc. 2002, 124, 6232–6233; b) J. L. Fillaut, J. Andries, J.
Perruchon, J. P. Desvergne, L. Toupet, L. Fadel, B. Zouchoune, J. Y.
Saillard, Inorg. Chem. 2007, 46, 5922–5932; c) D. A. Jose, P. Kar, D.
Koley, B. Ganguly, W. Thiel, H. N. Ghosh, A. Das, Inorg. Chem.
2007, 46, 5576–5584; d) L. Huynh, Z. Wang, J. Yang, V. Stoeva, A.
Lough, I. Manners, M. A. Winnik, Chem. Mater. 2005, 17, 4765–
4773; e) Q. Zhao, F. Y. Li, C. H. Huang, Chem. Soc. Rev. 2010, DOI:
10.1039/B915340C.
[6] a) Q. Zhao, T. Y. Cao, F. Y. Li, X. H. Li, H. Jing, T. Yi, C. H. Huang,
Organometallics 2007, 26, 2077–2081; b) Q. Zhao, S. J. Liu, F. Y. Li,
T. Yi, C. H. Huang, Dalton Trans. 2008, 3836–3840; c) Q. Zhao,
F. Y. Li, S. J. Liu, M. X. Yu, Z. Q. Liu, T. Yi, C. H. Huang, Inorg.
Chem. 2008, 47, 9256–9264; d) H. L. Chen, Q. Zhao, F. Y. Li, Y. B.
Wu, H. Yang, T. Yi, C. H. Huang, Inorg. Chem. 2007, 46, 11075–
11081.
[7] a) Y. You, S. Y. Park, Adv. Mater. 2008, 20, 3820–3826; b) S. B.
Zhao, T. McCormick, S. Wang, Inorg. Chem. 2007, 46, 10965–10967;
c) E. Sakuda, A. Funahashi, N. Kitamura, Inorg. Chem. 2006, 45,
10670–10677; d) Y. Sun, N. Ross, S. B. Zhao, K. Huszarik, W. L. Jia,
R. Y. Wang, D. Macartney, S. Wang, J. Am. Chem. Soc. 2007, 129,
7510–7511; e) S. T. Lam, N. Y. Zhu, V. W. W. Yam, Inorg. Chem.
2009, 48, 9664–9670; f) Y. L. Rao, S. Wang, Inorg. Chem. 2009, 48,
7698–7713; g) Z. M. Hudson, S. B. Zhao, R. Y. Wang, S. Wang,
Chem. Eur. J. 2009, 15, 6131; h) Y. Sun, S. Wang, Inorg. Chem. 2009,
48, 3755.
[8] N. Miyaura, A. Suzuki, J. Chem. Soc. Chem. Commun. 1979, 866–
867.
[9] Y. Z. Hu, G. Zhang, R. P. Thummel, Org. Lett. 2003, 5, 2251–2253.
[10] R. Stahl, C. Lambert, C. Kaiser, R. Wortmann, R. Jakober, Chem.
Eur. J. 2006, 12, 2358–2370.
[11] K. Nonoyama, Bull. Chem. Soc. Jpn. 1974, 47, 467–468.
[12] a) K. A. King, P. J. Spellane, R. J. Watts, J. Am. Chem. Soc. 1985,
107, 1431–1432; b) S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-
Razzaq, R. Kwong, I. Tsyba, M. Bortz, B. Mui, R. Bau, M. E.
Thompson, Inorg. Chem. 2001, 40, 1704–1711.
[13] a) A. Tsuboyama, H. Iwawaki, M. Furugori, T. Mukaide, J. Kamata-
ni, S. Igawa, T. Moriyama, S. Miura, T. Takiguchi, S. Okada, M.
Hoshino, K. Ueno, J. Am. Chem. Soc. 2003, 125, 12971–12979;
b) A. B. Tamayo, S. Garon, T. Sajoto, P. I. Djurovich, I. M. Tsyba, R.
Bau, M. E. Thompson, Inorg. Chem. 2005, 44, 8723–8732.
[14] Q. Zhao, S. J. Liu, M. Shi, C. M. Wang, M. X. Yu, L. Li, F. Y. Li, T.
Yi, C. H. Huang, Inorg. Chem. 2006, 45, 6152–6160.
[15] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wall-
ingford, CT, 2004.
[16] a) H. Y. Wang, G. Chen, Y. Liu, L. H. Hu, X. P. Xu, S. J. Ji, Dyes
Pigm. 2009, 83, 269–275; b) W. L. Yu, J. Pei, Y. Cao, W. Huang,
A. J. Heeger, Chem. Commun. 1999, 1837–1838.
Received: February 10, 2010
Published online: May 12, 2010
Chem. Eur. J. 2010, 16, 7125 – 7133
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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