Design and synthesis of luminescence chemosensors based on alkynyl phosphine gold(i)-copper(i) aggregates

Article abstract of DOI:10.1039/c1dt10197h

Receptor-containing polynuclear mixed-metal complexes of gold(i)-copper(i) 1-3 based on a [{Au₃Cu₂(CCPh)₆}Au ₃{PPh₂-C₆H₄-PPh₂} ₃]²⁺ (Au₆

Full text of DOI:10.1039/c1dt10197h

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PAPER
Design and synthesis of luminescence chemosensors based on alkynyl
phosphine gold(I)–copper(I) aggregates†
Xiaoming He, Nianyong Zhu and Vivian Wing-Wah Yam*
Received 4th February 2011, Accepted 6th July 2011
DOI: 10.1039/c1dt10197h
Receptor-containing polynuclear mixed-metal complexes of gold(I)–copper(I) 1–3 based on a
2
+
[
{Au
3
Cu
2
(C CPh)
6
}Au
3
{PPh
2
–C
6
H
4
–PPh
2
}
3
]
(Au
6
Cu ) core with benzo-15-crown-5, oligoether and
2
urea binding sites were designed and synthesized, respectively. These complexes exhibited remarkably
strong red emission at ca. 619–630 nm in dichloromethane solution at room temperature upon
photoexcitation at l > 400 nm, with the emission quantum yield in the range 0.59–0.85. The
cation-binding properties of 1 and 2 and the anion-binding properties of 3 were studied using UV-vis,
1
emission and H NMR techniques. Complex 1, with six benzo-15-crown-5 pendants, was found to show
+
+
+
+
+
a higher binding preference for K , with a selectivity trend of K ꢀ Cs > Na > Li . The addition of
+
+
+
+
metal ions (Li , Na , K and Cs ) to complex 1 led to a modest emission enhancement with a
concomitant slight blue shift in energy and well-defined isoemissive points, which is attributed to the
rigidity of the structure and the inhibited PET (photo-induced electron transfer) process from the
oxygen to the aggregate as a result of the binding of the metal ion. The six urea receptor groups on
complex 3 were found to form multiple hydrogen bonding interactions with anions, with the positive
charge providing additional electrostatic interaction for anion-binding. The anion selectivity of 3
-
-
-
-
-
follows the trend F > Cl ª H
2
PO > Br and the highest affinity towards F is attributed to the
stronger basicity of F , as well as its good size match with the cavity of the urea pocket.
4
-
Introduction
minescent metal ion sensors has been relatively less explored, the
6
7
8
main examples being of ruthenium(II), rhenium(I), iridium(III)
In supramolecular host–guest chemistry, the design of selec-
tive and sensitive ion receptors is of great importance, due
to their potential applications in ion transport, chemosensing
and especially in the field of biomedical and environmental
9
and platinum(II) complexes utilizing MLCT excited states for
luminescent signal transduction.
10
Luminescent polynuclear d metal complexes have attracted
increasing attention because of their potential applications in lu-
1,2
sciences. Macrocyclic crown ether and oligoether units have
been extensively utilized as the specific binding sites for alkali
10,11
minescence chemosensors, OLEDs or dopant emitters.
Gold(I)
complexes are one of the important classes, due to their in-
triguing photoluminescence behaviour and their propensity to
1
and alkaline earth metal ions. Urea has often been used as an
excellent hydrogen bond donor in the design of anion receptors.
Signal transduction is also important in the design of specific
chemosensors. Luminescence signaling has been widely used in
the design of chemosensors due to its high sensitivity and the
2,3
12
form aurophilic Au ◊ ◊ ◊ Au interactions. Many studies showed
that an increase in the Au ◊ ◊ ◊ Au interaction would lead to a
13
shift of the emission to lower energy. The ability of gold(I) to
form heterometallophilic Au ◊ ◊ ◊ M (M = Cu or Ag) interactions
4
simplicity of its equipment requirements. Although most studies
14
is also interesting. Abu–Salah and coworkers reported a series
on the design of luminescence probes for ion sensing in the past
have been focused on organic receptors based on polyaromatic
luminophores involving photoinduced electron transfer (PET)
10
of heteronuclear d metal alkynyl complexes, demonstrating the
presence and importance of both s- and p-bonding modes in
15
metal alkynyl systems. In these compounds, the emission can
5
processes, the utilization of transition metal complexes as lu-
be modified not only by the aurophilic Au ◊ ◊ ◊ Au interactions,
but also by the presence of heterometallophilic Au ◊ ◊ ◊ Cu or
Au ◊ ◊ ◊ Ag interactions. The photophysical properties of a series
Institute of Molecular Functional Materials (Areas of Excellence Scheme,
University Grants Committee, Hong Kong) and Department of Chemistry,
The University of Hong Kong, Pokfulam Road, Hong Kong, P.R. China.
E-mail: wwyam@hku.hk
of pentanuclear Au(I)–Cu(I) and Ag(I) mixed-metal alkynyl com-
n
plexes, [ Bu
4
N][Au
3
M
2
(C CC
6
H
4
R-p)
6
], (M = Cu, R = OMe,
n
n
n
O Bu, O Hex, Me, Et; M = Ag, R = Et, O Hex), have been
studied by us. Eisenberg and coworkers reported interesting
†
Electronic supplementary information (ESI) available. CCDC reference
16
number 811061. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1dt10197h
polymorphism of [PPN][Au Cu (1-ethynylcyclohexanol) ], and
3
2
6
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demonstrated that the polymorphs exhibit different emission en-
Results and discussion
ergies as a result of the different Au ◊ ◊ ◊ Au, Au ◊ ◊ ◊ Cu and Cu ◊ ◊ ◊ Cu
17
Synthesis and characterization
distances.
Recently, Koshevoy and coworkers reported an interesting
series of alkynyl-phosphine gold(I)–copper(I) aggregates that have
highly intense luminescence, with their luminescence quantum
Complexes 1–3 were synthesized according to a modification
18
of previously reported procedures and the synthetic route is
summarized in Scheme 1. Complexes S1–S3 were synthesized
according to a modification of the literature method by adding 1,4-
18
yields reaching a maximum value of 0.92. The metal-centered
triplet state of the heterometallic alkynyl aggregate was suggested
to play a key role in the observed phosphorescence. Variation
of the substituents with different electronic groups was found
to have relatively little effect on the structure, but displayed a
significant influence on their photophysical properties. In addition,
a decrease in the size of the metal aggregate has been found to
lead to an increase in efficiency and photostability, which has
been demonstrated by both experimental and theoretical studies.
Amongst all of the alkynyl–phosphine gold(I)–copper(I) aggre-
bis(diphenylphosphino)benzene to depolymerize [AuC CR]
which was prepared in situ by reacting [Au(tht)Cl] with the
corresponding HC CR in the presence of Et N. By adding a
stoichiometric amount of [Cu(CH CN) ]PF to the respective
μ
,
3
3
4
6
complexes S1–S3 in dichloromethane solution, bright orange to
red solutions with intense red emissions were observed. Complexes
1–3 were obtained as orange to red solids upon recrystallization
from dichloromethane–diethyl ether. All of the complexes were
1
31
characterized by H NMR, P NMR and FAB-MS and gave
satisfactory elemental analysis. The structure of complex 3 was
established by X-ray structure determination.
2
+
gates reported, [{Au
with the smallest Au
stable and effective luminophore.
3
Cu
2
(C CPh)
6
}Au
3
{PPh
2
–C
6
H
4
–PPh
2
}
3
] ,
6
Cu
2
cluster core, was found to be the most
18b
It is believed that such kinds of strongly emissive luminophores
could be explored for signal transduction in the design of
luminescence chemosensors via the PET (photoinduced electron
transfer) mechanism upon the introduction of some specific
X-Ray crystal structure determination of 3
The perspective drawing of the complex cation of 3 is depicted
in Fig. 1. The structure of complex 3 is similar to the reported
ion-binding groups to the [{Au
3
Cu
system. Herein, we report the design and synthesis of
aggregate-based complexes 1–3 with benzo-15-crown-5,
2
(C CPh)
6
}Au
3
{PPh
2
–C
6
H
4
–
2
+
2+
PPh
2
}
3
]
[{Au Cu (C CPh) }Au {PPh –C H –PPh } ] with a Au Cu
3
2
6
3
2
6
4
2
3
6
2
1
8
-
Au Cu
6
2
core, which has a central [Au Cu (C CR) ] “rod” wrapped
3
2
6
3
+
oligoether and urea binding sites, respectively (Scheme 1). The
photophysical and cation-binding properties of 1 and 2 and the
anion-binding properties of 3 have been studied using UV-vis,
by a [Ph P–C H –PPh Au] “belt”. Six urea receptor groups are
2
6
4
2
3
integrated into the luminescent Au Cu unit. It is expected that six
6
2
urea receptor groups provide a pocket that form multiple hydrogen
bonding interactions with anions.
1
emission and H NMR techniques.
Scheme 1 The synthetic route to 1–3.
9
704 | Dalton Trans., 2011, 40, 9703–9710
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of the phosphine and alkynyl ligands, while the lower-energy
absorption at ca. 400 nm and the tails extending to 550 nm are
likely to be ascribed to metal cluster-centered ds/dp transitions
due to the presence of the metal ◊ ◊ ◊ metal interaction, with some
mixing of metal to p*(C CR) metal-to-ligand charge transfer
(
MLCT) transitions.
In addition, complexes 1–3 gave remarkably strong red emission
at ca. 619–630 nm in dichloromethane solution at room tem-
perature upon photoexcitation at l > 400 nm (Fig. S2†). The
luminescence quantum yields of complexes 1–3 are in the range
0
.59–0.85. The long-wavelength emission with high luminescence
Fig. 1 A perspective drawing of the complex cation of 3. Thermal
ellipsoids are shown at the 30% probability level.
quantum yield make these complexes useful for application as
chemosensors. The emission lifetimes are found to be in the
microsecond range, which is suggestive of a triplet parentage. The
intense red emission was tentatively assigned to the metal cluster
Table 1 Selected bond lengths [ A˚ ] and bond angles [deg] for complex 3
with estimated standard deviations in parentheses
(
Au
6
Cu )-centered triplet emission. Complex 3 showed a slight
2
Selected bond lengths [ A˚ ]
blue shift in emission energy compared to those of complexes
1
and 2, which have strong electron-donating groups, similar to
Cu(1)–Au(1)
Cu(1)–Au(5)
Cu(2)–Au(3)
Au(1)–Au(5)
Au(3)–Au(4)
Au(5)–Au(6)
2.7691(15)
2.9329(15)
2.880415)
3.3363(8)
2.8594(9)
2.8654(7)
Cu(1)–Au(3)
Cu(2)–Au(5)
Au(1)–Au(2)
Au(1)–Au(3)
Au(3)–Au(5)
2.8830(15)
2.7821(14)
2.8656(7)
3.3684(8)
3.2645(10)
18c
those reported previously.
Ion-binding studies
Cation-binding of complexes 1 and 2. The cation-binding
ability of complexes 1 and 2 was investigated by luminescence
studies. In general, the addition of metal ions (Li , Na , K and
+
+
+
The selected bond lengths are tabulated in Table 1. Three short
Au ◊ ◊ ◊ Au contacts (2.8594, 2.8656 and 2.8654 A) between the
˚
+
Cs ) to complex 1 gave rise to a modest emission enhancement,
“
rod” and “belt” were observed, suggesting the “rod-and-belt”
with a concomitant slight blue shift in energy and well-defined
isoemissive points. Fig. 2 shows the emission spectral changes of
structure is stabilized by the aurophilic interactions. The structure
of the central [Au
reported pentanuclear clusters [Au
metal atoms are arranged at the vertices of the trigonal bipyramid,
in which two copper atoms occupy the apical positions, while the
three gold atoms form a triangle. Each gold(I) atom is s-bonded
to two alkynyl groups in an almost linear fashion, with the C–
-
+
3
Cu
2
(C CR)
6
] “rod” is very similar to the
complex 1 upon the addition of K in CH Cl –CH OH (1 : 1 v/v;
2
2
3
-
15,16
n
3
Cu
2
(C CPhR-4)
6
] .
The
0.1 M Bu NPF ). The inset shows the changes in the emission
4
6
+
intensity at 610 nm as a function of the added K concentration.
Such an enhancement in emission intensity could be rationalized
˚
Au–C angles in the range 1.946–2.036 A. On the other hand,
each copper(I) atom is unsymmetrically p-bonded to three alkynyl
groups. Six short Au ◊ ◊ ◊ Cu distances in the range 2.7691(15)–
2
.9329(15) were also observed, indicative of the presence of
heterometallic Au ◊ ◊ ◊ Cu interactions. Such short heterometallic
Au ◊ ◊ ◊ Cu contacts were also found in the previously reported
-
15,16
pentanuclear clusters [Au
3
Cu
2
(C CPhR-4) ] .
6
Electronic absorption and emission properties
In dichloromethane solution, complexes 1–3 exhibited yellow to
orange–yellow colors. Intense high-energy absorption bands at
2
60–310 nm and low-energy absorption bands at ca. 400 nm, with
tails to ca. 550 nm were observed (Fig. S1†). The photophysical
-7
Fig. 2 Emission spectral traces of 1 (2.88 ¥ 10 M) in CH
2
Cl
2
–MeOH
data are collected in Table 2. With reference to a previous work
n
+
(
1 : 1 v/v; 0.1 M Bu
4
NPF
6
) upon the addition of K . Excitation at 400 nm.
Inset: A plot of the emission intensity at 610 nm as a function of K
concentration and its theoretical fit for the 1 : 1 binding of complex 1 with
16
on alkynylgold(I) and copper(I) and the systematic study on the
+
18
related Au
6
Cu
2
system by Koshevoy, the high-energy absorption
+
bands are tentatively assigned as the intraligand p → p* transitions
K .
Table 2 Photophysical data for complexes 1–3
-5
3
-1
-1
Complex
Absorption l/nm (e¥10 /dm mol cm )
Emission lem/nm (t
0
/ms)
ø
em
1
2
3
264 (1.44), 310 (0.81), 400 (0.42)
264 (1.79), 290 (1.16), 402 (0.53)
266 (1.99), 304 (1.36), 398 (0.62)
630 (5.6)
630 (8.3)
619 (7.8)
0.85
0.72
0.59
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Table 3 Binding constants (log K
s
) of complex 1 for various metal ions
in CH Cl –CH OH (1 : 1, v/v) at 298 K
2
2
3
+
+
+
+
Li
Na
K
Cs
1
Too small to be determined 3.67 ± 0.04 6.81 ± 0.03 4.66 ± 0.10
by the increased rigidity of the structure and the inhibited PET
photo-induced electron transfer) process from the oxygen to the
(
+
aggregate upon binding of the metal ion. The addition of Na
and Cs also produced similar emission enhancement, as shown
+
in Fig. S3–S4.† However, few emission changes were observed for
+
+
Li , which may be due to the small binding affinity of 1 for Li as
a result of the poor size match. In our previous work on dinuclear
gold(I) complexes with crown ether pendants and the trinuclear
gold(I) complex with oligoether pendants, the metal binding could
force the gold(I) atoms into close proximity, which can lead to a
10a–d
large emission response in the lower-energy wavelength region.
However, in this work, no lower-energy emission bands were
observed for complexes 1 and 2 upon metal ion binding. The
reason might be due to the rather rigid structure of the aggregates,
which would not allow the gold(I) and copper(I) atoms in 1 and
2
to change readily upon binding, as compared to our previous
10a–d
1
systems.
Fig. 3 H NMR spectral changes of 1 (2.1 mM) in CDCl –CD OD (1 : 1
3
3
The emission titration data were found to show a close
agreement with the theoretical fit based on a 1 : 1 binding model.
v/v) upon the addition of various metal ions at room temperature.
+
+
+
The binding constants (log K
s
) of 1 toward Na , K and Cs
C
6
H
4
spacer. The set of high-field resonance signals are assigned to
-
were determined to be 3.67 ± 0.04, 6.81 ± 0.03 and 4.66 ± 0.10,
respectively, and are tabulated in Table 3. Complex 1 shows a
higher binding preference for the binding of metal ions with large
the benzo-15-crown-5 moieties in the [Au
3
Cu
2
(C CR)
6
] “rod”.
The addition of metal ions was found to lead to large changes in
the chemical shifts of the aromatic protons (H –H ) of the benzo-
15-crown-5 moieties, while almost no changes were observed on
a
c
+
+
+
+
+
sizes (K and Cs ), with a selectivity trend of K ꢀ Cs > Na >
+
3+
Li . Despite the well-known selectivity of benzo-15-crown-5 (1.70–
.20 A) for Na (1.94 A) due to the good size match between the
crown cavity and the Na ion, a trend that is not consistent with
that expected was observed. The high binding preference for K
the [Ph
2
P–C
6
H
4
–PPh
2
Au]
3
“belt”, indicating that metal ions are
and H were found to exhibit
+
˚
˚
2
bound to the crown units. Protons H
b
c
+
large downfield shifts with well-resolved doublet signals upon the
addition of alkali metal ions. In addition, metal ions with a large
+
+
+
+
˚
˚
(
2.66 A) and Cs (3.34 A), which are too large to fit into the
size (K and Cs ) showed more a significant effect on the downfield
shifts. The downfield shift of H and H upon cation-binding could
cavity size of benzo-15-crown-5, is suggestive of their binding to
the benzocrown moieties in a sandwiched or caged fashion.
The UV-vis spectrophotometric method was also used to
investigate the cation binding behavior of 1. However, very small
UV-vis spectral changes were observed for complex 1 upon the
addition of alkali metal ions (Fig. S5†).
b
c
be ascribed to the electron-withdrawing effect of the cation. The
more pronounced effect induced by larger size metal ions may be
due to the higher binding constants, as shown in Table 3. On the
contrary, the H proton resonance was found to show interesting
a
+
+
shifts. K and Cs with large sizes were found to lead to a large
+
The cation-binding properties of complex 2 were also inves-
tigated by emission spectroscopy. However, a slight emission
enhancement was observed upon the addition of metal ions. This
may be ascribed to the non-specific binding and floppy nature of
the oligoether receptors.
upfield shift of H
a large downfield shift instead. The different shift mode of H
may be attributed to the different binding mode of the metal ion
a
, while Na with a smaller size gave rise to
a
+
to 1. The downfield shift of H
explained by the electron-withdrawing effect of Na upon binding
into the crown cavity. The unusual upfield shifts of H induced by
a
caused by Na could be readily
+
1
The cation-binding properties of 1 were also studied using H
a
1
+
+
NMR spectroscopy. Fig. 3 shows the H NMR spectral changes
K and Cs are likely a consequence of the ring current effect
resulting from p-stacking in the sandwiched or caged binding
mode. Similar upfield shifts in related sandwiched structures have
of 1 upon the addition of an excess of different alkali metal ions
in CDCl
protons of complex 1 displayed a set of low-field resonance signals
d (ppm): 7.85, 7.61 and 7.41) and a set of high-field resonance
signals (d (ppm): 6.38 and 6.25). Based on the detailed NMR study
3
–CD OD (1 : 1, v/v) at room temperature. The aromatic
3
1
9
also been reported by us and Choi and Hamilton.
1
(
In addition, a variable-temperature H NMR study of complex
1 in the absence and presence of Cs was also performed (Fig.
S6†). Interestingly, in the presence of Cs , the signal at d 7.61 ppm
+
18b
+
by Koshevoy, the set of low-field signals can be assigned to the
3
+
Ph
2
P–C
6
H
4
–PPh
2
moieties in the [Ph
2
P–C
6
H
4
–PPh
2
Au]
3
“belt”,
(a mixture of para-H of the diphosphine and the C
6
4
H spacer) split
in which the signals at d 7.85 and 7.41 are assigned to the ortho-H
and meta-H of the diphosphine ligand and the signal at d 7.61
is assigned to the mixture of para-H of the diphosphine and the
into two signals with nearly a 1 : 1 ratio at 258 K. However, such
+
splitting was not observed in the absence of Cs . This splitting
+
in the presence of Cs at low temperature could be a result of
9
706 | Dalton Trans., 2011, 40, 9703–9710
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Table 4 Binding constants (log K ) of complex 3 for various anions in
s
CH
2
Cl
2
(1 : 1, v/v) at 298 K
F- Cl-
7.55 ± 0.19 6.82 ± 0.09
Br-
H
PO -
2
4
3
5.47 ± 0.12
6.70 ± 0.30
the unsymmetrical binding of the cation to the crown units on
one side and not the other, which caused the original signal at d
7
.61 ppm to split into two well-resolved signals at low temperature,
confirming the domination of the 1 : 1 binding mode. These signals,
together with the nice agreement of the experimental data with the
theoretical fit using the 1 : 1 binding model, are supportive of our
assignment.
-
7
Fig. 5 Emission spectral traces of 3 (3.72 ¥ 10 M) in CH
2
Cl
2
upon the
-
addition of F . Excitation at 400 nm. Inset: A plot of the emission intensity
at 600 nm as a function of F concentration and its theoretical fit for the
-
Anion-binding of complex 3. The anion-binding ability of
complex 3 was investigated by luminescence and UV-vis spec-
trophotometric methods. Fig. 4 shows the UV-vis spectral changes
-
1 : 1 binding of complex 3 with F .
1
-
-
H NMR spectroscopic experiments were also carried out. Fig. 6
shows the H NMR spectral changes of 3 in CD
, the H NMR signals
of the urea moieties were not well-resolved and the two NH
peaks were found to be masked by the aromatic signals of the
urea moiety. Large H NMR spectral changes of the urea moiety
were observed upon the addition of protic solvent CD
solution, while the proton signals of the
“belt” remained almost unchanged. The
OD led to well-resolved proton resonances of the
urea moieties and the disappearance of the NH signals as a result
of the fast exchange with the solvent. The addition of F also led
to large downfield shifts of the two NH protons, suggesting that
F would interact with 3 through hydrogen bonding interactions.
However, complex 3 is not very stable in the presence of a large
excess of anions (ca. 1000 equiv.) for a long period of time (ca.
12 h). Large emission quenching was observed. This may be due
to the extraction of the Cu ion by the large excess of anions and
cluster 3 to dinuclear gold(I)
complex S3, which can be confirmed by H NMR study. A similar
decomposition process for 3 can also be found in the H NMR
experiment using d -DMSO as the solvent.
of 3 upon the addition of F in CH
2
2
Cl . The addition of F
1
2
Cl
2
upon the
produced an observable absorbance enhancement at 274–450 nm,
with a clean isosbestic point at 274 nm, while the low-energy tail
at 450–550 nm remained unchanged. Fig. 5 shows the emission
-
1
addition of F and CD
3
OD. In CD
2
Cl
2
-
spectral changes of 3 upon addition of F in CH
2
Cl . The
2
1
-
addition of F also led to a modest enhancement of the emission
intensity. This enhancement in the emission intensity could also be
attributed to the increased rigidity of the molecule upon F binding
3
OD and
-
-
F ions to 3 in CD
2
Cl
2
3
+
[
Ph
2
P–C
6
H
4
–PPh
2
Au]
3
to the urea units. Similar emission changes were also observed
-
-
-
-
addition of CD
3
upon the addition of H
2
PO and Cl . For Br and I , only slight
4
emission changes were observed as a result of the weak hydrogen
bonding interaction. The emission titration data showed a nice fit
to a 1 : 1 binding model. Table 4 shows the binding constants of
-
-
complex 3 for various anions. The binding constants (log K
s
) of
were determined to be 7.55 ±
.19, 6.82 ± 0.09, 5.47 ± 0.12 and 6.70 ± 0.30, respectively. The
-
-
-
-
3
toward F , Cl , Br and H
2
PO
4
0
-
-
-
anion selectivity of 3 follows the trend of F > Cl ª H
Br , suggesting that 3 can serve as a selective receptor for F . The
highest affinity towards F could be attributed to the stronger
basicity of F , which can establish a stronger hydrogen bonding
2
PO
4
>
+
-
-
-
the decomposition of the Au
6
Cu
2
1
-
1
interaction with urea group, as well as its good size match with
the cavity of the urea pocket. Fabbrizzi and coworkers studied
the correlation of selectivity with basicity in detail, revealing that
anion basicity plays an important role in determining the anion
6
Conclusion
3a
selectivity.
In summary, we designed and synthesized three receptor-
containing polynuclear mixed-metal complexes of gold(I)–
copper(I) 1–3 based on the [{Au
3
Cu
2
(C CPh)
6
}Au
3
{PPh
2
–
2
+
C
6
H
4
–PPh (Au Cu ) core with benzo-15-crown-5, oligoether
2
}
3
]
6
2
and urea binding sites, respectively. Their photophysical and
ion-binding properties were studied. These complexes exhib-
ited remarkably strong red emission at ca. 619–630 nm in
dichloromethane solution at room temperature, with the emission
quantum yield in the range 0.59–0.85. The highly emissive Au
6
Cu
2
aggregate luminophore has proved to be an effective signal
transduction unit in the design of luminescence chemosensors.
Through the judicious introduction of specific ion-binding groups
to the strongly emissive Au
6
Cu aggregate, different selective
2
luminescence chemosensors could be realized. Complex 1, with six
benzo-15-crown-5 pendants, was found to show a higher binding
-6
+
Fig. 4 UV-vis spectral changes of complex 3 (7.45 ¥ 10 M) in CH
2
Cl
2
preference for K , while complex 3, with six urea receptor groups,
n
-
upon the addition of Bu
4
NF at 298 K.
showed the highest binding affinity towards F .
This journal is © The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 9703–9710 | 9707

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1
-
2 2 3
Fig. 6 H NMR spectral changes of 3 in CD Cl (a) in the absence and the presence of (b) F and (c) CD OD.
Experimental section
[(PPh
.17 mmol) was added to a dichloromethane solution of 4-
ethynylbenzo-15-crown-5 (L1) (50 mg, 0.17 mmol) and Et N (120
2
C
6
H
4
PPh
2
)(AuC CB15C5) ] (S1). [Au(tht)Cl] (55 mg,
2
0
Materials and reagents
3
ml, 0.85 mmol) under a nitrogen atmosphere, and the mixture
was stirred at 0 C for 2 h. 1,4-Bis(diphenylphosphino)benzene
Tetra-n-butylammonium fluoride, tetra-n-butylammonium chlo-
ride, tetra-n-butylammonium bromide, and tetra-n-butylammo-
nium phosphate were purchased from Fluka. Lithium perchlorate,
sodium perchlorate, potassium hexafluorophosphate, phenyl
isocyanate and tetra-n-butylammonium hexafluorophosphate
were purchased from Aldrich Chemical Company and the
latter was recrystallized three times from hot absolute
ethanol and dried under vacuum for 12 h prior to use. 1,4-
◦
(38.2 mg, 0.085 mmol) was then added to the solution and the
reaction mixture was allowed to stir for 2 h. The solvent was then
removed under reduced pressure and the residue was recrystallized
from dichloromethane–diethyl ether to give S1 as a pale yellow
1
solid. Yield: 61 mg, 50%. H NMR (400 MHz, CDCl
3
, 298 K,
–), 3.88 (m, 8 H;
–), 6.74 (d, J = 8.3 Hz, 2 H; –
–), 7.02 (d, J = 1.8 Hz, 2 H; –C –), 7.07 (dd, J = 8.3
and 1.8 Hz, 2 H; –C –), 7.46–7.60 (m, 24 H; –C – and –
). P NMR (202 MHz, CDCl , relative to 85% H PO ): d
2.5. FAB-MS: m/z 1131 [M - L] , 1423 [M] , 1446 [M + Na] .
Elemental analysis, anal. found (%): C, 50.66; H, 4.20. Calcd for
·CH Cl : C, 50.18; H, 4.28.
relative to Me
4
Si): d 3.76 (m, 16 H; –OCH
2
–
OCH –), 4.10 (m, 8 H; –OCH
2
2
20
Bis(diphenylphosphino)benzene,
4-ethynylbenzo-15-crown-5
C
6
H
3
6
H
3
9b
10c
(
L1), 1-ethynyl-4-(2-(2-methoxyethoxy)ethoxy)benzene) (L2),
H
3
6
H
4
21
22
6
4
-ethynyaniline, cesium triflate, [Cu(CH
3
CN)
4
]PF
6
,
gold(I)
3
1
PPh
4
2
3
3
4
23
18
acetylene polymer [AuC CR] and complexes S1–S3 and 1–3
were synthesized according to modified reported procedures.
All solvents were purified and distilled using standard proce-
+
+
+
C
62
H
62Au
2
O
10
P
2
2
2
24
dures before use. All other reagents were of analytical grade
and were used as received. All reactions were carried out
under an inert atmosphere of nitrogen using standard Schlenk
techniques.
[(PPh C H PPh )[AuC CC H O(CH CH O) CH ] ]
2
6
4
2
6
4
2
2
2
3 2
(S2).
This was synthesized according to the procedure for S1, except L2
(37.7 mg, 0.17 mmol) was used instead of L1. Recrystallization
from dichloromethane–diethyl ether gave S2 as a white solid.
1
Yield: 98 mg, 90%. H NMR (400 MHz, CDCl
3
, 298 K, relative
Synthesis
to Me Si): d 3.38 (s, 6 H; –OCH ), 3.57 (m, 4 H; –OCH –),
4
3
2
3
–
2
.71 (m, 4 H; –OCH
2
–), 3.84 (m, 4 H; –OCH
2
–), 4.12 (m, 4 H;
HC CC
HC CC
CH Cl was slowly added phenyl isocyanate (0.3 g, 2.56 mmol)
in CH Cl (10 ml) over a period of 10 min and the mixture was
heated to reflux overnight under a nitrogen atmosphere. The
precipitate was collected by filtration and washed twice with
6
H
4
NHCONHC
6
H
5
(L3). To
a
solution of
OCH
8 H; –PC
, relative to 85% H
2
–), 6.80 (d, J = 8.8 Hz, 4 H; –C
P–, –C C– and –PPh
PO ): d 42.5. FAB-MS: m/z 1059 [M -
6
H
4
C
C-), 7.40–7.60 (m,
6
H
4
NH (0.3 g, 2.56 mmol) in 40 ml of anhydrous
2
3
1
6
H
4
6
H
4
C
2
). P NMR (202 MHz,
2
2
CDCl
3
3
4
2
2
+
+
+
L] , 1278 [M] , 1475 [M + Au] . Elemental analysis, anal. found
(%): C, 50.44; H, 4.19. Calcd for C56
H
54Au
2
O
6
P
2
·CH
2
2
Cl : C,
50.20; H, 4.14.
CH
2
Cl
H NMR (400 MHz, DMSO-d
s, 1 H; C CH), 6.98 (t, J = 7.4 Hz, 1 H; –C
2
to yield the product as a yellow solid. Yield: 0.45 g, 75%.
, 298 K, relative to Me Si): d 4.04
–), 7.29 (t, J =
–), 7.46 (m,
–), 8.72 (s, 1 H; –NH), 8.88 (s, 1 H; –NH).
1
6
4
[(PPh PPh
2
C
6
H
4
2
)(AuC CC
6
H
4
NHCONHC
6
H
5
)
2
]
(S3).
(
6
H
5
This was synthesized according to the procedure for S1, except
L3 (40 mg, 0.17 mmol) was used instead of L1. Recrystallization
from dichloromethane–diethyl ether gave S3 as a pale yellow
7
.4 Hz, 2 H; –C
6
H
5
–), 7.35 (d, J = 7.8 Hz, 2 H; –C
6
H
4
4
H; –C – and –C
6
H
4
6
H
5
+
1
FAB-MS: m/z 236 [M] .
solid. Yield: 89 mg, 80%. H NMR (400 MHz, DMSO-d
6
, 298 K,
9
708 | Dalton Trans., 2011, 40, 9703–9710
This journal is © The Royal Society of Chemistry 2011

View Article Online
relative to Me
8
8
4
Si): d 6.97 (t, J = 7.3 Hz, 2 H; –C
.6 Hz, 4 H; –C ), 7.28 (t, J = 7.6 Hz, 4 H; –C
.6 Hz, 4 H; –C ), 7.44 (d, J = 7.6 Hz, 4 H; –C
and –C –), 8.69 (s, 2 H; –NH), 8.74 (s, 2 H;
NH). P NMR (202 MHz, d -DMSO, relative to 85% H PO ):
6
H
5
), 7.22 (d, J =
were recorded on a Bruker Avance 400 FT-NMR spectrometer
6
H
4
6
H
5
), 7.38 (d, J =
with chemical shifts reported relative to 85% H
3
PO . Positive-ion
4
6
H
4
6
H
5
), 7.57–7.72
fast atom bombardment (FAB) mass spectra were recorded on a
Finnigan MAT95 mass spectrometer. Elemental analysis of the
new complexes was performed on a Carlo Erba 1106 elemental
analyzer at the Institute of Chemistry of the Chinese Academy of
Sciences in Beijing.
(
–
m, 24 H; PPh
2
6
H
4
3
1
6
3
4
+
+
d 42.1. FAB-MS: m/z 1312 [M] , 1075 [M - L] . Elemental
analysis, anal. found (%): C, 53.35; H, 3.53; N, 4.17. Calcd for
C
60
H
46Au
2
N
4
O
2
P
2
·0.5CH
2
Cl
2
: C, 53.69; H, 3.50; N, 4.14.
Steady-state excitation and emission spectra were recorded on
a Spex Fluorolog-3 Model FL3-211 fluorescence spectrofluorom-
eter equipped with a R2658P PMT detector. All solutions for
photophysical studies were prepared under a high vacuum in
[
(PPh
2
C
6
H
4
PPh Au
2
)
3
3
{Au
3
Cu (C CB15C5)
2
6
}][PF
6
]
2
(1).
This was synthesized according to a modification of a reported
procedure.
dichloromethane (3 ml) was added dropwise to a solution of
S1 (58 mg, 0.18 mmol) in dichloromethane (8 ml) to afford
a transparent red solution. The solution was removed under
vacuum and product was recrystallized from dichloromethane–
18
[Cu(CH
3
CN)
4
]PF
6
(10 mg, 0.027 mmol) in
3
a 10-cm round-bottomed flask equipped with a sidearm 1-cm
fluorescence cuvette and sealed from the atmosphere by a Rotaflo
HP6/6 quick-release Teflon stopper. Solutions were rigorously
degassed on a high-vacuum line in a two-compartment cell
with no less than four successive freeze–pump–thaw cycles. The
excitation source used was the 355-nm output (third harmonic,
diethyl ether to give 1 as a red crystal. Yield: 41 mg, 65%.
1
H NMR (400 MHz, CDCl
3
, 298 K, relative to Me
–), 3.66 (m, 12 H; –OCH –), 3.73 (m,
–), 3.87 (m, 12 H; –OCH –), 4.02 (m, 12 H;
–), 6.19 (6 H; –C –), 6.30 (m, 12 H; –C –), 7.35
PC PPh ), 7.50–7.58 (m, 24 H;
), 7.82 (m, 24 H; Ph
202 MHz, CDCl , relative to 85% H
m/z 1620. Elemental analysis, anal. found (%): C, 46.87; H, 3.85.
4
Si): d
8
ns) of a Spectra-Physics Quanta-Ray Q-switched GCR-150
3
4
–
.26 (m, 12 H; –OCH
8 H; –OCH
OCH
2
2
pulsed Nd:YAG laser (10 Hz). Luminescence decay signals were
detected by a Hamamatsu R928 photomultiplier tube, recorded
2
2
2
6
H
3
6
H
3
-
1
on a Tektronix Model TDS-620 A (500 MHz, 2 GS s ) digital
(
t, J = 7.7 Hz, 24 H; Ph
2
6
H
4
2
oscilloscope, and analyzed by using a program for exponential
fits.
3
1
Ph PC PPh
2
6
H
4
2
2
PC
PO
6
H
4
PPh
2
). P NMR
(
3
3
4
): d 44.3. FAB-MS:
Binding constant determination
Calcd for C186
H
186Au
6
O
30
P
8
Cu
{ Au
(2). This was synthesized according to the proce-
2
F
12·CH
2
Cl
2
: C, 47.08; H, 3.97.
[
( PPh
2
C
6
H
4
PPh
2
)
3
Au
3
3
Cu
2
[ C CC
6
H
4
O ( CH CH O )
2
2
2
-
The emission spectral titration for binding constant determination
was performed on Spex Fluorolog-3 Model FL3-211 fluorescence
spectrofluorometer. Binding constants for 1 : 1 complexation were
CH
3
]
6
}][PF
]
6 2
dure for 1, except S2 (52 mg, 0.18 mmol) was used instead of
S1. Recrystallization from dichloromethane–diethyl ether gave 2
as a red plate crystal. Yield: 35%. H NMR (400 MHz, CDCl
25
obtained by a nonlinear least-squares fit of the emission intensity
1
3
,
(I) versus the concentration of ions added (C ) according to the
A
2
1
98 K, relative to Me
2 H; –OCH –), 3.73 (m, 12 H; –OCH
–), 4.04 (m, 12 H; –OCH –), 6.34 (d, J = 8.7 Hz, 12
H; –C CC –), 6.53 (d, J = 8.7 Hz, 12 H; –C CC –),
.33 (t, J = 7.7 Hz, 24 H; –Ph PC PPh –), 7.55 (m, 24 H; –
Ph PC PPh –), 7.81 (m, 24 H; –Ph PC
202 MHz, CDCl , relative to 85% H PO ): d 44.1. FAB-MS: m/z
] . Elemental analysis, anal. found (%): C, 46.97;
Cu Cl : C, 46.78; H, 3.81.
·CH
4
Si): d 3.41 (s, 18 H; –OCH
3
), 3.61 (m,
following equation:
2
2
–), 3.86 (m, 12 H; –
OCH
2
2
Ilim −I0
2
1/ 2
I = I +
[C +CM +1/ K −[(C +C +1/ K ) −4C C ] ]
0 s 0 M s 0 M
0
H
4
2C
0
6
H
4
6
7
2
6
H
4
2
3
1
2
6
H
4
2
2
6
H
4
PPh –). P NMR
2
where I and I are the emission intensity the complex at a
0
(
3
+
3
4
selected wavelength in the absence and presence of the ions,
respectively, [C ] is the total concentration of the complex, [C ] is
the concentration of the ion, Ilim is the limiting value of emission
2
1982 [M - 2PF
6
0
M
3.85. C168
H
162Au
6
2
F
12
O
18
P
8
2
2
intensity in the presence of excess ion and K is the stability
constant.
s
[
(PPh
2
C
6
H
4
PPh Cu (C CC NHCONHC
2
)
3
Au
3
{Au
3
2
6
H
4
6
H
5
)
6
}]-
[
PF
]
6 2
(3). This was synthesized according to the procedure
for 1, except S3 (53 mg, 0.18 mmol) was used instead of S1.
Recrystallization from dichloromethane–diethyl ether gave 3 as
X-Ray crystallography
1
a red crystal. Yield: 70%. H NMR (400 MHz, CD
2
Cl
Si): d 6.54 (d, J = 8.5 Hz, 2 H;),
.87 (d, J = 8.5 Hz, 2 H;), 7.01 (t, J = Hz, 1 H;), 7.20–7.28 (m, 4
H;), 7.38 (t, J = 7.5 Hz, 4 H;), 7.57 (t, J = 7.6 Hz, 2 H;), 7.62 (m, 2
2
–CD
3
OD
A single crystal of 3 was obtained by vapor diffusion of diethyl
ether into a concentrated solution of 3 in dichloromethane–
methane (3 : 1, v/v). The structure was solved by direct methods
employing SHELXS-97 program on PC. Au, Cu, P and many
non-H atoms were located according to the direct methods.
The positions of the other non-hydrogen atoms were found
after successful refinement by full-matrix least-squares using
program SHELXL-97 on PC. There was one formula unit in
the asymmetric unit. Two PF anions were located. Two halves
of methanol and two water O atoms were located, in which the
two water O atoms may form H-bonding to NH groups and the
two halves of methanol located inside the “cages”. All benzene
rings were constrained to be regular hexagon rings with edges
(
2 : 1, v/v), 298 K, relative to Me
4
6
26
2
+
H;), 7.84 (m, 4 H;). FAB-MS: m/z. 2030 [M-2PF
6
] . Elemental
analysis, anal. found (%): C, 49.42; H, 3.35; N, 3.89. Calcd for
C
180
H
138Au
6
Cu
2
N
12
O
6
P
8
F
12·CH
3
OH·2H
2
O: C, 49.21; H, 3.33; N,
3.80.
26
6
Physical measurements and instrumentation
The UV-vis spectra were recorded on a Hewlett–Packard 8452 A
1
diode array spectrophotometer. H NMR spectra with chemical
shifts relative to tetramethylsilane (Me Si) were recorded on a
4
3
1
˚
Bruker Avance 400 FT-NMR spectrometer. P NMR spectra
of 1.39 A.
This journal is © The Royal Society of Chemistry 2011
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View Article Online
Acknowledgements
Chen, Y. H. Hu, Y. M. Cheng, K. S. Chen, G. H. Lee, Y. Chi and P. T.
Chou, Org. Biomol. Chem., 2006, 4, 98.
(a) V. W. W. Yam, R. P. L. Tang, K. M. C. Wong, X. X. Lu, K. K.
Cheung and N. Zhu, Chem.–Eur. J., 2002, 8, 4066; (b) W. S. Tang, X. X.
Lu, K. M. C. Wong and V. W. W. Yam, J. Mater. Chem., 2005, 15, 2714.
9
V. W.-W. Y. acknowledges the support from The University
of Hong Kong under the Distinguished Research Achievement
Award Scheme. Technical assistance on variable-temperature in
1
0 (a) V. W. W. Yam, C. K. Li and C. L. Chan, Angew. Chem., Int. Ed.,
1998, 37, 2857; (b) C. K. Li, X. X. Lu, K. M. C. Wong, C. L. Chan,
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E. C. C. Cheng, N. Zhu and V. W. W. Yam, Chem. Commun., 2009, 4016;
1
H NMR experiments and final editing by Dr T. K. M. Lee
and Dr A. Y. Y. Tam is gratefully acknowledged. This work
is supported by the University Grants Committee Areas of
Excellence Scheme (AoE/P-03/08) and General Research Fund
(
d) X. M. He, W. H. Lam, N. Zhu and V. W. W. Yam, Chem.–Eur. J.,
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GRF) grant from the Research Grants Council of Hong Kong
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710 | Dalton Trans., 2011, 40, 9703–9710
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