A near-infrared phosphorescent probe for F- based on a cationic iridium(III) complex with triarylboron moieties

Article abstract of DOI:10.1007/s11426-011-4359-y

In this work, a near-infrared (NIR) phosphorescent probe for F^- based on a cationic Ir(III) complex [Ir(Bpq)₂(quqo)]PF₆ (1) with dimesitylboryl (Mes2B) groups on the cyclometalated CN ligands (Bpq) and 2-(quinolin-2-yl)qui

Full text of DOI:10.1007/s11426-011-4359-y

SCIENCE CHINA
Chemistry
November 2011 Vol.54 No.11: 1750–1758
doi: 10.1007/s11426-011-4359-y
• ARTICLES •
A near-infrared phosphorescent probe for F based on a cationic
iridium(III) complex with triarylboron moieties
XU WenJuan, LIU ShuJuan, ZHAO Qiang*, MA TingChun, SUN Shi,
ZHAO XinYan & HUANG Wei*
State Key Laboratory for Organic Electronics & Information Displays (KLOEID); Institute of Advanced Materials (IAM),
Nanjing University of Posts and Telecommunications, Nanjing 210046, China
Received February 27, 2011; accepted April 8, 2011; published online September 5, 2011
In this work, a near-infrared (NIR) phosphorescent probe for F based on a cationic Ir(III) complex [Ir(Bpq)2(quqo)]PF6 (1)
with dimesitylboryl (Mes2B) groups on the cyclometalated C^N ligands (Bpq) and 2-(quinolin-2-yl)quinoxaline (quqo) as N^N
ligand was designed and synthesized. The excited state properties of 1 were investigated in detail using molecular orbital cal-
culations and experimental methods. Upon excitation, complex 1 shows NIR phosphorescent emission around 680 nm. Inter-
estingly, the complex can be excited with long wavelength around 610 nm. Such long-wavelength excitation can reduce the
background emission interference and improve the signal-to-noise ratio. Furthermore, the selective binding between boron at-
om and F can give rise to the quenching of emission and realize the near-infrared phosphorescent sensing for F. We wish that
the results reported herein will be helpful for the further design of excellent near-infrared phosphorescent probes based on
heavy-metal complexes.
F sensor, iridium(III) complex, NIR-infrared, phosphorescent, triarylboron
selectivity. And some excellent F receptors and probes
1 Introduction
have been reported [18–21]. Due to the Lewis acidity of
boron center, triarylboranes with bulky aryl substitutes can
react with small nucleophilic anions including F to afford
fluoroborate anions. The bulky aryl substitutes, such as me-
sityl group, play a very important role in governing the se-
lectivity of triarylborane receptors for small F. In addition,
triarylborane derivatives exhibit relatively intense fluores-
cent characteristics due to the conjugation of p(B) with the
π-electron system in the aryl group (p(B)- conjugation),
giving rise to unique electronic structures. In view of these,
luminescent triarylborane derivatives as F probes have re-
ceived widespread research interest recently [22–24].
Up to now, the signal of most reported fluorescent probes
is visible light. As we all know, the probes with a near-
infrared (NIR) optical response could avoid interference
from endogenous chromophores and would be more useful
in complex systems, such as biological system [25, 26].
Fluoride ion (F) plays an essential role in the health, medi-
cal, and environmental sciences [1–6]. Hence, it is very
important to develop excellent probes for F. Up to now, a
large number of fluorescent probes based on organic lumi-
nophores have been designed to detect this important ana-
lyst [7–13], owing to its high sensitivity, easy visualization,
and short response time for detection. In most cases, the
binding sites of the probes for F consist of amide, urea,
thiourea, guanidinium, or pyrrole functionalities that are
capable of hydrogen bonding with F [14–17]. The selectiv-
ity of the probes based on this strategy is, however, often
not good. Thus, it is very meaningful to exploit new strate-
gies to design fluorescent probes for sensing F with high
*Corresponding author (email: iamqzhao@njupt.edu.cn; wei-huang@njupt.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2011
chem.scichina.com www.springerlink.com

Xu WJ, et al. Sci China Chem November (2011) Vol.54 No.11
1751
Moreover, they can be operated with inexpensive and com-
pact NIR diodes, lasers or light-emitting diodes [26]. When
applied in biological systems, the light in NIR region
around 650–900 nm is poorly absorbed by biomolecules,
and it can penetrate deeply into tissues. Furthermore, there
is also less autofluorescence in this region, and so the char-
acteristics of these dyes are favorable for in vivo imaging.
Hence, it is a very important topic to develop NIR dyes ap-
plied in sensing and bioimaging.
Currently, most reported or commercial NIR probes are
based on organic luminophores. In addition to organic lu-
minophores, luminescent metal complexes are another im-
portant class of probe materials [27–33]. Among them,
heavy-metal complexes with phosphorescent emission are
one important kind of luminescent metal complexes due to
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 excitation
in the visible range and relatively long lifetimes compared
to those of purely organic luminophores. The advantageous
phosphorescent emission is beneficial for chemical or bio-
logical detection. Introducing dimesitylboryl (Mes2B)
groups into the ligands of heavy-metal complexes can real-
ize phosphorescent detection for F through the specific
interaction of boron atoms with F, which can induce varia-
tions in the excited state properties of heavy-metal com-
plexes. More recently, several phosphorescent probes for F
based on heavy-metal complexes, such as Ir(III), Pt(III) and
Re(I) complexes containing Mes2B group have been re-
ported by us and other groups [34–41]. However, no NIR
phosphorescent probe for F based on this design strategy
has been reported up to now.
In order to realize the near-infrared phosphorescent F
probe, two points should be considered. One is that the
probe should contain the receptor for F, such as Mes2B
group. The other is that the conjugation length of ligands
should be increased in order to shift the emission wave-
length to the NIR region. Cationic Ir(III) complexes with
two cyclometalated C^N ligands and one neutral N^N lig-
and are excellent phosphorescent materials. Their excited
state properties can be determined by both C^N and N^N
ligands. Thus, it is very convenient to design NIR phospho-
rescent probe based on cationic Ir(III) complexes by modi-
fying the chemical structures of both C^N and N^N ligands.
The excited state energy level of complexes can be de-
creased by extending the conjugation length of both C^N
and N^N ligands, inducing the significant red-shift of emis-
sion wavelength. In addition, the receptor for the analyte
can be introduced into C^N or N^N ligands to realize the
detection. Herein, we designed and synthesized a novel cat-
ionic Ir(III) complex [Ir(Bpq)2(quqo)]PF6 (1) with Mes2B
groups on the C^N ligands (Bpq) (see Scheme 1). On the
one hand, Mes2B groups can act as the receptor for F. On
the other hand, the conjugation length of C^N ligand can be
increased through the p(B)- conjugation, inducing the
decrease of energy level and red-shift of emission wave-
length. Furthermore, 2-(quinolin-2-yl)quinoxaline (quqo)
with low energy level was chosen as N^N ligand in order to
Scheme 1 The synthetic route of complex 1.

1752
Xu WJ, et al. Sci China Chem November (2011) Vol.54 No.11
shift the emission wavelength to the longer region [42]. Be-
cause of the synergetic effect of N^N ligand quqo and C^N
ligand Bpq, complex 1 showed a near-infrared phosphores-
cent emission. The selective interaction of boron and F can
induce the variation in emission, realizing the NIR phos-
phorescent probe for F.
2.4 Synthesis
2-(4-Bromophenyl)quinoline (Brpq), 2-(4-(dimesitylboryl)-
phenyl)-quinoline (Bpq), and 2-(quinolin-2-yl)quinoxaline
(quqo) were prepared according to the literature procedures,
[34, 42] and the synthetic route is shown in Scheme 1.
Synthesis of complex 1
Complex 1 was synthesized through a standard two-step
procedure according to the literature method. 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
mixture was refluxed for 24 h. After cooling, the orange
solid precipitate was filtered to give crude cyclometalated
Ir(III) chloro-bridged dimer. The solution of cyclometalated
Ir(III) chloro-bridged dimer (0.079 mmol) and quqo (0.158
mmol) in CH2Cl2/MeOH [30 mL, 2:1 (v/v)] was heated to
reflux. After 4 h, the black solution was cooled down to
room temperature and then a 10-fold excess of potassium
hexafluorophosphate was added. The suspension was stirred
for 2 h and then was filtered to remove insoluble inorganic
salts. The solution was evaporated to dryness under reduced
pressure. It was chromatographed by using CH2Cl2/acetone
2 Experimental
2.1 General
NMR spectra were recorded on a Bruker Ultra Shield Plus
400 MHz NMR instruments (1H: 400 MHz, 13C: 100 MHz).
Mass spectra were obtained on a Thermo Scientific ESI-MS
spectrometer. The UV-vis absorption spectra were recorded
on a Shimadzu UV-3600 UV-vis-NIR spectrophotometer.
Lifetime studies were performed by an Edinburgh LFS-920
spectrometer with a hydrogen-filled excitation source. The
data were analyzed by iterative convolution of the lumines-
cence decay profile with the instrument response function
using a software package provided by Edinburgh Instru-
ments. Photoluminescent spectra were measured using a
RF-5301PC Spectrofluorophotometer. The elemental analy-
sis was performed using Vario Macro apparatus (Germany).
The quantum efficiency was determined by exciting the sam-
ple at 400 nm with the use of fac-Ir(ppy)3 (fac-tris(2-phenyl-
pyridine) iridium) as the standard ( = 0.86) in CH2Cl2
solution [43].
1
(50:1) to afford black solid in a 70% yield. H NMR (400
MHz, CDCl3):  = 9.41 (s, 1H), 8.58 (d, J = 8.6 Hz, 1H),
8.16 (d, J = 8.6 Hz, 2H), 7.85–7.94 (m, 3H), 7.43–7.75 (m,
10H), 7.24–7.36 (m, 4H), 7.14–7.17 (m, 2H), 6.93–7.03(m,
2H), 6.98 (t, J = 7.9 Hz, 1H), 6.68 (t, J = 7.9 Hz, 1H), 6.60
(s, 4H), 6.48 (s, 4H), 6.35 (s, 1H), 6.21 (s, 1H), 2.30 (s, 6H),
2.19 (s, 6H), 1.61–1.66 (m, 24H); 13C NMR (101 MHz,
CDCl3):  = 169.30, 168.84, 156.92, 153.61, 148.41, 147.78,
147.39, 147.27, 147.12, 146.55, 146.29, 144.77, 144.19,
141.85, 140.74, 140.35, 140.26, 140.22, 139.68, 139.59,
139.18, 138.36, 138.33, 132.41, 131.81, 131.45, 131.17,
130.84, 130.67, 130.58, 130.10, 129.32, 129.22, 128.83,
128.00, 127.85, 127.60, 127.55, 127.41, 127.31, 127.05,
126.02, 125.57, 124.91, 123.92, 120.95, 117.10, 116.54,
23.10, 23.05, 21.43, 21.34; MS (ESI-MS) [m/z]: 1354.25
(1-PF6)+; Anal calcd (%) for C83H73N5F6B2PIr: C 66.49, H
4.91, N 4.67. Found: C 66.15, H 4.92, N 4.69.
2.2 Computational details
The ground-state and the lowest-lying triplet excited-state
geometries were optimized by density functional theory
(DFT) with Becke’s LYP (B3LYP) exchange-correlation
functional and the unrestricted B3LYP (UB3LYP) approach,
respectively. On the basis of ground- and excited-state op-
timization, the time-dependent DFT (TDDFT) approach
associated with the polarized continuum model (PCM) in
dichloromethane (CH2Cl2) media was carried out to obtain
the vertical excitation energies of singlet (Sn) and triplet (Tn)
states. The calculation was performed using the Gaussian 03
suite of programs [44]. 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 highest
occupied molecular orbitals and lowest unoccupied molec-
ular orbits (HOMOs and LUMOs) were plotted.
3 Results and discussion
3.1 Synthesis and characterization of complex 1
Scheme 1 shows the synthetic route of complex 1. The N^N
ligand quqo and cyclometalated C^N ligand Bpq were pre-
pared according to the literature procedures [34, 42]. The
dinuclear cyclometalated Ir(III) chloro-bridged precursor
[Ir(Bpq)2Cl]2 with Bpq as cyclometalated ligand was syn-
thesized using the same method as that reported by Nono-
yama [45]. The cationic Ir(III) complex was then routinely
synthesized with a high yield of 70% by reacting cyclomet-
alated Ir(III) chloro-bridged precursor with ligand quqo, and
the synthetic route is shown in Scheme 1. The structure of
2.3 Materials
All starting materials and reagents, unless otherwise speci-
fied, were purchased from commercial suppliers and used
without further purification. All solvents were purified be-
fore use.

Xu WJ, et al. Sci China Chem November (2011) Vol.54 No.11
1753
complex 1 was characterized by 1H NMR spectroscopy, 13C
NMR spectroscopy, elemental analysis, and ESI-MS spec-
trometry.
Table 1 Calculated energy levels of the singlet states and lowest triplet
state for complex 1
Ecal a) (eV)
1.97
F b)
0.0020
cal a) (nm)
State
S1
Excitation
HOMO→LUMO (70%)
HOMO→LUMO (57%)
HOMO-9→LUMO (30%)
HOMO-2→LUMO (46%)
HOMO-10→LUMO (47%)
HOMO→LUMO+1 (65%)
HOMO-1→LUMO (14%)
HOMO→LUMO+1 (19%)
HOMO-1→LUMO (59%)
HOMO-2→LUMO (47%)
HOMO-10→LUMO (43%)
HOMO→LUMO+2 (67%)
HOMO-2→LUMO (47%)
HOMO-10→LUMO (43%)
HOMO-5→LUMO (57%)
HOMO-4→LUMO (34%)
HOMO-6→LUMO (55%)
HOMO-5→LUMO (33%)
HOMO→LUMO (70%)
630
S2
S3
S4
S5
2.50
2.58
2.61
2.61
497
481
475
474
0.0035
0.0004
0.0568
0.0050
3.2 Photophysical properties of complex 1
The UV-vis absorption spectrum of complex 1 was investi-
gated and is shown in Figure 1. The complex displayed in-
tense absorption bands below 400 nm, moderately intense
absorption bands in the range of 400–525 nm, and weak
absorption bands above 525 nm. The absorption bands at λ
< 400 nm related to the singlet ligand-centered -* transi-
tions from Bpq and quqo ligands. According to the previous
study, both ligand-to-ligand charge transfer (LLCT) and
metal-to-ligand charge transfer (MLCT) transitions may
contribute to the visible-region absorption bands. Therefore,
we believe that the moderately intense absorptions at ca.
400–525 nm and weak absorptions above 525 nm may re-
ceive contributions from singlet and triplet LLCT and
MLCT for complex 1. Interestingly, low-energy absorption
bands around 610 nm were observed evidently, providing
the possibility of detection using long-wavelength excita-
tion.
To better understand the absorption properties of 1, DFT
and TDDFT calculations for this complex were performed
employing the Gaussian-03 package. The ground-state and
the lowest-lying triplet excited-state geometries were opti-
mized by DFT with B3LYP exchange-correlation functional
and UB3LYP approach, respectively. On the basis of
ground- and excited-state optimization, TDDFT approach
associated with the PCM in CH2Cl2 media was carried out
to obtain the vertical excitation energies of singlet (Sn) and
triplet (Tn) states. From the calculated results, no obvious
bond length differences between the lowest singlet state and
the lowest triplet state are observed for 1, and the frontier
molecular orbital compositions of excited-state are similar
to those of ground state. The frontier molecular orbital
compositions and energy levels are given in Table 1 and
Table 2. According to the calculated oscillator strength and
energy level, the weak absorption band at 610 nm originates
S6
S7
S8
2.64
2.68
2.73
470
463
454
0.0011
0.0074
0.0008
S9
2.74
453
0.0009
S10
T1
2.75
1.46
451
849
0.0054

a) Ecal: calculated energy, cal: calculated wavelength; b) f: calculated
oscillator strength.
from S1 state, namely HOMO→LUMO (70%) transitions.
From the corresponding molecular orbital distributions
(shown in Table 2), we can see that the HOMO distribution
primarily resides on the Mes2B fragments of ligand Bpq and
the LUMO distribution is dominated by N^N ligand quqo.
So, this band can be mainly assigned to the LLCT transition
from the Mes2B group on C^N ligands to the N^N ligand
quqo. The extended conjugation length of N^N ligand,
which decreases the LUMO energy level, is responsible for
the long-wavelength absorption. The moderately intense
absorption band at 450 nm can be attributed to S4
state from
HOMO–LUMO+1 (65%) and HOMO–1–LUMO (14%)
transitions according to the calculated oscillator strength and
energy level. This band can be assigned to a mixture of the
intraligand charge transfer (ILCT) transition from Mes2B
group to 2-phenylquinoline moiety on C^N ligands and
LLCT transition from Mes2B group to N^N ligand quqo.
The photoluminescence (PL) spectrum of complex 1 in
CH2Cl2 solution was measured. From Figure 1, we can see
that complex 1 showed NIR emission around 680 nm. The
observed emission lifetime of 1 in air-balanced CH2Cl2 so-
lution is 0.2 s, indicating the phosphorescent nature of the
emission. At room temperature in CH2Cl2 solution, upon
excitation at different wavelength of 379, 450 and 613 nm
respectively, complex 1 showed the similar NIR phospho-
rescence. So, there is no dependence of emission band of
complex 1 on excitation wavelength. With fac-Ir(ppy)3 as
the standard, we measured the room-temperature phospho-
rescent quantum yields () of complex 1 in CH2Cl2 solution.
Complex 1 shows quantum efficiency of 0.02. Furthermore,
the excitation spectrum of complex 1 monitored at 680 nm
was investigated. As shown from the excitation spectrum
(see Figure 2), we can see that the major excitation peak is
located at 613 nm, further demonstrating the possibility of
detection using long-wavelength excitation. And such long
Figure 1 Absorption and PL spectra (ex = 450 nm) of 1 (20 M) in
CH2Cl2 solution.

1754
Xu WJ, et al. Sci China Chem November (2011) Vol.54 No.11
the HOMO→LUMO transition. The discrepancies between
the calculated values and experimental data may be at-
tributed to DFT method, which generally gives a smaller
HOMO-LUMO gap for molecules and thus generates
smaller excitation energies, especially for larger conjugated
systems and charge-transfer complexes in excited states [46,
47]. According to the HOMO and LUMO distributions
shown in Table 2, we can conclude that the NIR emission of
complex 1 can be assigned to the LLCT transition from
Mes2B groups to N^N ligand quqo.
One of the challenges in the design of luminescent
probes, particularly those aimed at complex system detec-
tion and practical application, is to shift the excitation
wavelength from UV region to long-wavelength range be-
cause many background fluorescence cannot be excited by
long wavelength light and long wavelength excitation re-
quires cheaper optical cells and optics. Herein, we chose
blue-emitting ligand Bpq as fluorescent noise to demon-
strate the advantage of long excitation and emission wave-
lengths of complex 1 applied in detection. We mixed Bpq
and complex 1 together in CH2Cl2 solution and then meas-
ured its emission spectra excited at UV wavelength of 360
Figure 2 The emission (ex = 610 nm) and excitation spectra (em = 680
nm) of complex 1 in CH2Cl2 solution.
excitation wavelength is beneficial for the detection in the
complex system. In order to clarify the origin of emission at
680 nm, the energy of triplet states was calculated. The cal-
culated maximum emission band (T1 state) of 1 is centered
at 849 nm, which exhibits a red-shift of 169 nm compared
to the experimental value (680 nm), and can be assigned to
Table 2 Calculated molecular orbits of complex 1
LUMO+2
LUMO+1
LUMO
HOMO
HOMO-1
HOMO-2
HOMO-4
HOMO-5
HOMO-6
HOMO-9
HOMO-10

Xu WJ, et al. Sci China Chem November (2011) Vol.54 No.11
1755
nm and visible light of 610 nm, respectively. The emission
spectra are shown in Figure 3. From Figure 3, we can see
that the solution showed strong blue emission at 425 nm
from Bpq and very weak emission at 680 nm from complex
1 when excited at 360 nm. This indicated that the target
phosphorescent signal at 680 nm was contaminated by the
fluorescent noise of Bpq. In order to purify the signal,
long-wavelength excitation of 610 nm was applied. From
Figure 3 we can see that the sample effectively eliminates
the fluorescent noise, and thus gives the clean phosphores-
cent signal at 680 nm. Hence, the reduced background
emission interference and improved signal-to-noise ratio
were realized for complex 1 utilizing the long wavelength
excitation.
Figure 4 Change in the UV-vis absorption spectra of complex 1 (20 M)
in a CH2Cl2 solution with various amounts of F.
3.3 Optical responses of complex 1 to F
In view of specific interaction between F and boron center,
the response of complex 1 to F was investigated through
UV-vis absorption and emission spectra. Figure 4 shows the
variation in the absorption spectra of complex 1 upon the
addition of F–. The absorbance peaks at 365 and 613 nm
decreased gradually. The variation in the PL spectra with
613 nm as excitation wavelength is shown in Figure 5. Up-
on addition of F to the CH2Cl2 solution of complex 1, the
NIR phosphorescent emission intensity around 680 nm de-
creased gradually, and completely quenched eventually.
Hence, complex 1 realizes the ON-OFF-type NIR phospho-
rescent detection for F.
Figure 5 Change in the emission spectra of complex 1 (20 M) in
CH2Cl2 solution with various amounts of F (ex = 613 nm).
As shown by emission titration curves in Figure 6, after
the addition of approximately 2 equivalents of F, the emis-
sion intensity ratio of I/I0 at 680 nm reaches the saturated
point. Considering that there are two boron centers in one
complex molecule, it is possible for complex 1 to form a 1:2
complex with 2 equivalent of F because the two Mes2B
groups are electronically separated in the ground state and
spatially distant from each other. The stability constants for
the binding of one and two F to complex 1 (H) in CH2Cl2
solution were determined from the emission titration data.
Figure 6 Phosphorescent titration profile (dot) and its fitting curve (solid
line) of emission intensity at 680 nm versus the equivalent of F of i com-
plex 1 in CH2Cl2 solution (20 M).
Fitting the emission changes at wavelengths of 680 nm ac-
cording to ref. [48], the binding constants (K1 and K2) of
complex 1 to F were determined to be 2.64 × 106 and 2.12 ×
104 M1, respectively (see Figure 6), which are similar to the
values reported previously for boryl-based fluorescent and
phosphorescent receptors [11, 34].
To better understand the sensing mechanism of complex
Figure 3 The emission spectra of mixed free ligand Bpq (blue emission)
and complex 1 in CH2Cl2 solution with different excitation wavelengths.
1 to F, the lowest-lying triplet excited-state geometry was

1756
Xu WJ, et al. Sci China Chem November (2011) Vol.54 No.11
Table 3 Calculated molecular orbits of 1-2F
HOMO
LUMO
optimized by DFT with UB3LYP approach. On the basis of
excited-state optimization, TDDFT approach associated
with the PCM in CH2Cl2 media was carried out to obtain the
vertical excitation energies of triplet (Tn) states. The HOMO
and LUMO distributions are shown in Table 3. According
to the calculation results, the T1 state for the adduct 1-2F
originates from HOMO→LUMO (70%) transition. The
HOMO distribution primarily resides on the Mes2B-F–
fragments, and the LUMO distribution resides on the N^N
ligand (quqo). Maybe the binding of boron center with F
blocks the charge transfer from Mes2B groups to N^N lig-
and responsible for the emission in free 1 and changes the
excited-state property of complex, quenching its emission.
Figure 8 Emission response of probe 1 (20 M) in the presence of vari-
ous anions (4 equiv) in CH2Cl2 solutions. Bars represent the ratio of emis-
sion intensity at  = 680 nm (I/I0). Black and red represent I/I0 before and
after the addition of anions, respectively. Blue bar represents I/I0 after
addition of F to the solution of complex 1 containing other anions. 1 F; 2
Cl; 3 Br; 4 I; 5 NO3; 6 H2PO4; 7 CH3COO; 8 ClO4.
alyte of interest over a complex background of potentially
competing species is a challenge in probe development.
Thus, the competition experiment was also carried out by
adding F- to the solutions of complex 1 in the presence of
other anions. As shown in Figures 7 and 8, whether in the
absence or presence of other anions, obvious spectral
changes were observed for complex 1 upon addition of F,
indicating that the sensing of F by complex 1 is hardly af-
fected by other anions.
3.4 Selectivity
The binding studies of probe 1 were extended to other ani-
ons in order to investigate the selectivity. As shown in Fig-
ure 7 from the absorption spectra, only the addition of F
results in prominent change of A/A0 at 367 nm, whereas the
addition of other anions (Cl, Br, ClO4, NO3, H2PO4,
CH3COO) causes little changes. From the emission spectra
(see Figure 8), the addition of most other anions caused
little changes, and only I showed some change in emission
spectra. Therefore, probe 1 displayed a high selectivity in
sensing F. Similarly, achieving high selectivity for the an-
4 Conclusions
In summary, we designed and synthesized a novel NIR-
emitting cationic Ir(III) complex with C^N ligands contain-
ing dimesitylboryl groups and extended N^N ligand. Upon
photoexcitation, the complex shows NIR phosphorescent
emission around 680 nm. Interestingly, the complex can be
excited with long wavelength around 610 nm, which can
reduce the background emission interference and improve
the signal-to-noise ratio. Through the selective binding be-
tween boron centers and F, an ON-OFF-type NIR phos-
phorescent probe was realized. Considering the advantages
of near-infrared and phosphorescent signals in sensing, we
wish that the results reported herein will be helpful for the
further design of excellent near-infrared phosphorescent
probes based on heavy-metal complexes.
This work was financially supported by the National Basic Research
Program of China (973 Program, 2009CB930601), National Natural
Science Foundation of China (50803028, 20804019 and 61006007),
Natural Science Foundation of Jiangsu Province of China (BK2009427),
Natural Science Fund for Universities in Jiangsu (10KJB430010), Scien-
tific and Technological Activities for Returned Scholars in Nanjing City
(NJ209001), and Nanjing University of Posts and Telecommunications
(NY208045).
Figure 7 UV-vis spectral response of complex 1 (20 M) in the presence
of various anions (4 equiv) in CH2Cl2 solution. Bars represent the ratio of
absorbances at  = 367 nm (A/A0). Black and red represent A/A0 before and
after the addition of anions, respectively. Blue bar represents A/A0 after
addition of F to the solution of complex 1 containing other anions. 1 F; 2
Cl; 3 Br; 4 I; 5 NO3; 6 H2PO4; 7 CH3COO; 8 ClO4.

Xu WJ, et al. Sci China Chem November (2011) Vol.54 No.11
1757
1
2
Beer PD, Gale PA. Anion recognition and sensing: The state of the
art and future perspectives. Angew Chem Int Ed, 2001, 40: 486–516
Martinez-Manez R, Sancenon F. Fluorogenic and chromogenic
chemosensors and reagents for anions. Chem Rev, 2003, 103:
4419–4476
Bowman-James K. Alfred Werner revisited: The coordination
chemistry of anions. Acc Chem Res, 2005, 38: 671–678
Amendola V, Esteban-Gómez D, Fabbrizzi L, Licchelli M. What
anions do to N- H-containing receptors. Acc Chem Res, 2006, 39:
343–353
Gale PA. Structural and molecular recognition studies with acyclic
anion receptors. Acc Chem Res, 2006, 39: 465–475
Cametti M, Rissanen K. Recognition and sensing of fluoride anion.
Chem Commun, 2009: 2809–2829
Boiocchi M, Del Boca L, Gómez DE, Fabbrizzi L, Licchelli M,
Monzani E. Nature of urea- fluoride interaction: Incipient and
definitive proton transfer. J Am Chem Soc, 2004, 126: 16507–16514
Kang SO, VanderVelde D, Powell D, Bowman-James K. Fluoride-
facilitated deuterium exchange from DMSO-d6 to polyamide-based
cryptands. J Am Chem Soc, 2004, 126: 12272–12273
sensing by boron-containing pi-electron systems. J Am Chem Soc,
2001, 123: 11372–11375
25 Patonay G, Antoine MD. Near-infrared fluorogenic labels––New
approach to an old problem. Anal Chem, 1991, 63: A321–A326
26 Fabian J, Nakazumi H, Matsuoka M. Near-infrared absorbing dyes.
Chem Rev, 1992, 92: 1197–1226
27 Hudnall TW, Gabbai FP. Ammonium boranes for the selective
complexation of cyanide or fluoride ions in water. J Am Chem Soc,
2007, 129: 11978–11986
28 You YM, Park SY. A Phosphorescent Ir(III) complex for selective
fluoride ion sensing with a high signal-to-noise ratio. Adv Mater,
2008, 20: 3820–3826
29 Sakuda E, Funahashi A, Kitamura N. Synthesis and spectroscopic
properties of platinum(II) terpyridine complexes having an arylborane
charge transfer unit. Inorg Chem, 2006, 45: 10670–10677
30 Zhao Q, Li FY, Huang CH. Phosphorescent chemosensors based on
heavy-metal complexes. Chem Soc Rev, 2010, 39: 3007–3030
31 Zhao Q, Cao TY, Li FY, Li XH, Jing H, Yi T, Huang CH. A highly
selective and multisignaling optical-electrochemical sensor for Hg2+
based on a phosphorescent iridium(III) complex. Organometallics,
2007, 26: 2077–2081
32 Zhao Q, Liu SJ, Li FY, Yi T, Huang CH. Multisignaling detection of
Hg2+ based on a phosphorescent iridium(III) complex. Dalton Trans,
2008: 3836–3840
33 Chen HL, Zhao Q, Wu YB, Li FY, Yang H, Yi T, Huang CH. Selective
phosphorescence chemosensor for homocysteine based on an
iridium(III) complex. Inorg Chem, 2007, 46: 11075–11081
34 Zhao Q, Li FY, Liu SJ, Yu MX, Liu ZQ, Yi T, Huang CH. Highly
selective phosphorescent chemosensor for fluoride based on an
iridium(III) complex containing arylborane units. Inorg Chem, 2008,
47: 9256–9264
3
4
5
6
7
8
9
Kang SO, Powell D, Day VW, Bowman-James K. Trapped bifluoride.
Angew Chem Int Ed, 2006, 45: 1921–1925
10 Lee MH, Agou T, Kobayashi J, Kawashima T, Gabba FP. Fluoride
ion complexation by a cationic borane in aqueous solution. Chem
Commun, 2007: 1133–1135
11 Liu XY, Bai DR, Wang SN. Charge-transfer emission in nonplanar
three-coordinate organoboron compounds for fluorescent sensing of
fluoride. Angew Chem Int Ed, 2006, 45: 5475–5478
12 Parab K, Venkatasubbaiah K, Jäkle F. Luminescent triarylborane-
functionalized polystyrene: Synthesis, photophysical characterization,
and anion-binding studies. J Am Chem Soc, 2006, 128: 12879–12885
13 Ros-Lis JV, Martínez-Máñez R, Sancenón M, Soto J, Rurack K,
Weißshoff H. Signalling mechanisms in anion-responsive push-pull
chromophores: The hydrogen-bonding, deprotonation and anion-
exchange chemistry of functionalized azo dyes. Eur J Org Chem,
2007: 2449–2458
35 Xu WJ, Liu SJ, Zhao XY, Sun S, Cheng S, Ma TC, Sun HB, Zhao Q,
Huang W. Cationic iridium(III) complex containing both triarylboron
and carbazole moieties as a ratiometric fluoride probe that utilizes a
switchable triplet-singlet emission. Chem Eur J, 2010, 16: 7125–7133
36 Zhao SB, McCormick T, Wang S. Ambient-temperature metal-to-
ligand charge-transfer phosphorescence facilitated by triarylboron:
Bnpa and its metal complexes. Inorg Chem, 2007, 46: 10965–
10967
14 Gale PA, Garcia-Garrido SE, Garric J. Anion receptors based on
organic frameworks: Highlights from 2005 and 2006. Chem Soc Rev,
2007
15 Miyaji H, Sato W, Sessler JL. Naked-eye detection of anions in
dichloromethane: Colorimetric anion sensors based on calix[4]pyrrole.
Angew Chem Int Ed, 2000, 39: 1777–1780
16 Schmidtchen FP, Berger M. Artificial organic host molecules for
anions. Chem Rev, 1997, 97: 1609–1646
37 Sun Y, Ross N, Zhao SB, Huszarik K, Jia WL, Wang RY, Macartney
D, Wang SN. Enhancing electron accepting ability of triarylboron via
pi-conjugation with 2,2′-bipy and metal chelation: 5,5′-Bis(BMes(2))-
2,2′-bipy and its metal complexes. J Am Chem Soc, 2007, 129:
7510–7512
17 Arnendola V, Bonizzoni M, Esteban-Gomez D, Fabbrizzi L, Licchelli
M, Sancenon F, Taglietti A. Some guidelines for the design of anion
receptors. Coordin Chem Rev, 2006, 250: 1451–1470
18 Lin ZH, Ou SJ, Duan CY, Zhang RG, Bai ZP. Naked-eye detection
of fluoride ion in water: A remarkably selective easy-to-prepare test
paper. Chem Commun, 2006: 624–626
19 Palacios MA, Nishiyabu R, Marquez M, Anzenbacher P. Supramo-
lecular chemistry approach to the design of a high-resolution sensor
array for multianion detection in water. J Am Chem Soc, 2007, 129:
7538–7544
20 Aydogan A, Coady DJ, Kim SK, Akar A, Bielawski CW, Marquez M,
Sessler JL. Poly(methyl methacrylate)s with pendant calixpyrroles
and crown ethers: Polymeric extractants for Potassium halides.
Angew Chem Int Ed, 2008, 47: 9648–9652
21 Hu R, Feng JA, Hu DH, Wang SQ, Li SY, Li Y, Yang GQ. A rapid
aqueous fluoride ion sensor with dual output modes. Angew Chem Int
Ed, 2010, 49: 4915–4918
22 Kubo Y, Yamamoto M, Ikeda M, Takeuchi M, Shinkai S, Yamaguchi
S, Tamao K. A colorimetric and ratiometric fluorescent chemosensor
with three emission changes: Fluoride ion sensing by a triarylborane-
porphyrin conjugate. Angew Chem Int Ed, 2003, 42: 2036–2040
23 Liu ZQ, Shi M, Li FY, Fang Q, Chen ZH, Yi T, Huang CH. Highly
selective two-photon chemosensors for fluoride derived from organic
boranes. Org Lett, 2005, 7: 5481–5484
38 Lam ST, Zhu NAY, Yam VWW. Synthesis and characterization of
luminescent rhenium(I) tricarbonyl diimine complexes with a triaryl-
boron moiety and the study of their fluoride ion-binding properties.
Inorg Chem, 2009, 48: 9664–9670
39 Rao YL, Wang SN. Impact of constitutional isomers of (BMes(2))
phenylpyridine on structure, stability, phosphorescence, and lewis
acidity of mononuclear and dinuclear Pt(II) complexes. Inorg Chem,
2009, 48: 7698–7713
40 Hudson ZM, Zhao SB, Wang RY, Wang SN. Switchable ambient-
temperature singlet-triplet dual emission in nonconjugated donor-
acceptor triarylboron-Pt-II complexes. Chem Eur J, 2009, 15: 6131–
6137
41 Sun Y, Wang SN. Conjugated triarylboryl donor-acceptor systems
supported by 2,2'-Bipyridine: Metal chelation impact on intraligand
charger transfer emission, electron accepting ability, and “turn-on”
fluoride sensing. Inorg Chem, 2009, 48: 3755–3767
42 Zhao Q, Liu SJ, Shi M, Wang CM, Yu MX, Li L, Li FY, Yi T,
Huang CH. Series of new cationic iridium(III) complexes with
tunable emission wavelength and excited state properties: Structures,
theoretical calculations, and photophysical and electrochemical
properties. Inorg Chem, 2006, 45: 6152–6160
43 Endo A, Suzuki K, Yoshihara T, Tobita S, Yahiro M, Adachi C.
Measurement of photoluminescence efficiency of Ir(III) phenylpyri-
dine derivatives in solution and solid-state films. Chem Phys Lett,
2008, 460: 155–157
24 Yamaguchi S, Akiyama S, Tamao K. Colorimetric fluoride ion

1758
Xu WJ, et al. Sci China Chem November (2011) Vol.54 No.11
44 Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb JRC,
Montgomery JA, Vreven T, Kudin KN, Burant JC, Millam JM,
Iyengar SS, Tomasi J, Barone V, Mennucci B, Cossi M, Scalmani G,
Rega N, Petersson GA, Nakatsuji H, Hada M, Ehara M, Toyota K, 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. Cioslowski, B. B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, 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 03, revision C.02.
Gaussian, Inc.: Wallingford, CT. 2003
45 Nonoyama M. [Benzo[h]quinolin-10-yl-N]iridium(III) complexes.
Bull Chem Soc Jpn, 1974, 47: 767–768
46 Zhao Q, Liu SJ, Sun S, Wang CM, Sun HB, Li FY, Fan QL, Huang
W. DFT/TDDFT investigation of the modulation of photochromic
properties in an organoboron-based diarylethene by fluoride ions.
Chemphyschem, 2011, 12: 313–321
47 Chen RF, Yin J, Zhang SL, Ling QD, Huang W. Theoretical studies
of the structural, electronic, and optical properties of phosphafluo-
renes. J Phys Chem A, 2010, 114: 3655–3667
48 Connors KA. Binding Constants: The Measurement of Molecular Co-
mplex Stability Constants. New York: John Wiley and Sonsm 1987. 161