Synthesis, characterization, structure, and selective Cu2+ sensing studies of an alkynylgold(I) Complex containing the dipicolylamine receptor

Article abstract of DOI:10.1021/om900148g

A novel DPA-containing alkynylgold(I) complex has been successfully synthesized and structurally characterized. The complex has been shown to exhibit rich photoluminescence property and to function as a selective sensor for Cu^2-, as revealed by

Full text of DOI:10.1021/om900148g

Organometallics 2009, 28, 3621–3624 3621
DOI: 10.1021/om900148g
Synthesis, Characterization, Structure, and Selective Cu2+ Sensing
Studies of an Alkynylgold(I) Complex Containing the
Dipicolylamine Receptor
Xiaoming He, Nianyong Zhu, and Vivian Wing-Wah Yam*
Centre for Carbon-Rich Molecular and Nano-Scale Metal-Based Materials Research,
Department of Chemistry, and HKU-CAS Joint Laboratory on New Materials, The University of Hong
Kong, Pokfulam Road, Hong Kong, People’s Republic of China
Received February 24, 2009
Summary: A novel DPA-containing alkynylgold(I) complex has
been successfully synthesized and structurally characterized. The
complex has been shown to exhibit rich photoluminescence prop-
erty and to function as a selective sensor for Cu2+, as revealed by
the large UV-vis change and significant emission quenching. The
recognition event was also found to show complete reversibility,
with the revival of the luminescence signal upon addition of EDTA.
The development of gold(I) chemistry has attracted grow-
ing interest in the past two decades, due to the attractive
Au Au interactions.1,2 Gold(I) alkynyl compounds are of
3 3 3
particular interest, not only due to their stability and ease of
preparation, but also because of their rich photophysical
properties, such as photoluminescence2-6 and optical non-
linearity.7 Introduction of gold(I) to the π-conjugated un-
saturated alkynyl ligand has recently been shown to induce
long-lived phosphorescence, which allows the time-resolved
discrimination of key luminescent processes, as a result of the
heavy metal atom effect, which enhances the spin-orbital
coupling.5c,5d In addition, the d10 closed-shell electronic
configuration of gold(I) does not allow the existence of
low-lying d-d excited states, and hence the lifetime and
luminescent triplet excited states would not be affected by
an internal quenching mechanism. Due to its linear geometry
and rigidity, together with the aurophilic nature of gold, a
number of supramolecular structures based on gold(I) alky-
nyl complexes have been designed and reported by us2-4 and
others,5,6 many of which show unique luminescence proper-
*Corresponding author. E-mail: wwyam@hku.hk.
(1) (a) Schmidbaur, H. Chem. Soc. Rev. 1995, 24, 391. (b) Schmidbaur,
H. Gold Bull. 2000, 33, 3. (c) Pyykko, P. Angew. Chem., Int. Ed. 2004, 43,
¨
¨
4412. (d) Pyykko, P.; Zhao, Y. Angew. Chem., Int. Ed. 1991, 30, 604.
(e) McCleskey, T. M.; Gray, H. B. Inorg. Chem. 1992, 31, 1733.
(f) Vickery, J. C.; Olmstead, M. M.; Fung, E. Y.; Balch, A. L. Angew.
Chem., Int. Ed. 1997, 36, 1179. (g) van Zyl, W. E.; Lopez-de-Luzuriaga,
J. M.; Mohamed, A. A.; Staples, R. J.; Fackler, J. P., Jr. Inorg. Chem.
2002, 41, 4579.
(2) (a) Yam, V. W. W.; Cheng, E. C. C. Chem. Soc. Rev. 2008, 37,
1806. (b) Yam, V. W. W.; Cheng, E. C. C. Top. Curr. Chem. 2007, 281,
269.
(3) (a) Yam, V. W. W.; Choi, S. W. K. J. Chem. Soc., Dalton Trans.
1996, 4227. (b) Yam, V. W. W.; Choi, S. W. K.; Cheung, K. K.
Organometallics 1996, 15, 1734. (c) Tang, H. S.; Zhu, N.; Yam, V. W.
W. Organometallics 2006, 26, 22. (d) Yam, V. W. W.; Cheung, K. L.;
Cheng, E. C. C.; Zhu, N.; Cheung, K. K. J. Chem. Soc., Dalton Trans.
2003, 1830. (e) Yam, V. W. W.; Cheung, K. L.; Yip, S. K.; Cheung, K. K.
J. Organomet. Chem. 2003, 681, 196. (f) Yip, S. K.; Lam, W. H.; Zhu, N.;
Yam, V. W. W. Inorg. Chim. Acta 2006, 359, 3639.
(4) (a) Yip, S. K.; Cheng, E. C. C.; Yuan, L. H.; Zhou, N.; Yam, V. W.
W. Angew. Chem., Int. Ed. 2004, 43, 4954. (b) Yam, V. W. W.; Cheung,
K. L.; Yuan, L. H.; Wong, K. M. C.; Cheung, K. K. Chem. Commun.
2000, 1513. (c) Yam, V. W. W.; Yip, S. K.; Yuan, L. H.; Cheung, K. L.;
Zhou, N.; Cheung, K. K. Organometallics 2003, 22, 2630. (d) Lu, X. X.;
Li, C. K.; Cheng, E. C. C.; Zhu, N.; Yam, V. W. W. Inorg. Chem. 2004,
43, 2225.
(5) (a) Li, D.; Hong, X.; Che, C. M.; Lo, W. C.; Peng, S. M. J. Chem.
Soc., Dalton Trans. 1993, 2929. (b) Che, C. M.; Yip, H. K.; Lo, W. C.;
Peng, S. W. Polyhedron 1994, 13, 887. (c) Che, C. M.; Chao, H. Y.;
Miskowski, V. M.; Li, Y.; Cheung, K. K. J. Am. Chem. Soc. 2001, 123,
4985. (d) Chao, H. Y.; Lu, W.; Li, Y.; Chan, M. C. W.; Che, C. M.;
Cheung, K. K.; Zhu, N. J. Am. Chem. Soc. 2002, 124, 14696.
(6) (a) Mingos, D. M. P.; Yan, J.; Menzer, S.; Williams, D. J. Angew.
Chem., Int. Ed. 1995, 34, 1894. (b) Puddephatt, R. J. Coord. Chem. Rev.
2001, 216-217, 313. (c) McArdle, C. P.; Van, S.; Jennings, M. C.;
Puddephatt, R. J. J. Am. Chem. Soc. 2002, 124, 3959. (d) Irwin, M. J.;
Vittal, J. J.; Puddephatt, R. J. Organometallics 1997, 16, 3541.
(e) Vicente, J.; Chicote, M. T.; Abrisqueta, M. D.; Jones, P. G.
Organometallics 1997, 16, 5628. (f) Bruce, M. I.; Hall, B. C.; Skelton,
B. W.; Smith, M. E.; White, A. H. J. Chem. Soc., Dalton Trans. 2002,
995. (g) Abu-Salah, O. M.; Al-Ohaly, A.; Knobler, C. B. J. Chem. Soc.,
Chem.Commun. 1985, 1502. (h) Koshevoy, I. O.; Koshinen, L.; Haukka,
M.; Tunik, S. P.; Serdobintsev, P. Y.; Melnikov, A. S.; Pakkanen, T. A.
Angew. Chem., Int. Ed. 2008, 47, 3942. (i) Koshevoy, I. O.; Karttunen,
A. J.; Tunik, S. P.; Haukka, M.; Selivanov, S. I.; Melnikov, A. S.;
Serdobintsev, P. Y.; Khodorkovskiy, M. A.; Pakkanen, T. A. Inorg.
Chem. 2008, 47, 9478. (j) de la Riva, H.; Nieuwhuyzen, M.; Fierro,
C. M.; Raithby, P. R.; Male, L.; Lagunas, M. C. Inorg. Chem. 2006, 45,
1418. (k) Wei, Q. H.; Zhang, L. Y.; Yin, G. Q.; Shi, L. X.; Chen, Z. N. J.
Am. Chem. Soc. 2004, 126, 9940.
ties that are strongly influenced by the presence of Au Au
interactions.
3 3 3
In the field of supramolecular and host-guest chemistry,
there has been a growing interest in the search for host
molecules that can selectively recognize specific guest mole-
cules through measurable photophysical changes. The sen-
sing receptor for Cu2+ is of particular interest due to the fact
that this metal ion is not only a commonly found metal
pollutant but also an essential trace element in the biological
system, particularly as one of the major sources of oxidative
stress that is closely related to the neurogenerative diseases.8
However, the development of a selective sensor for Cu2+ is
rather rare,9a-9c when compared to other biologically rele-
vant metal ions, including alkali ions (Na+, K+),9d alkaline
earth metal ions (Mg2+ and Ca2+),9e and other d-block ions,
such as Zn2+ 9f,9g
Effective signal transduction plays an
.
important role in the design of ion-specific chemosensors,
and luminescence technology has been widely used due to its
high sensitivity and the simplicity of its equipment require-
ment.10 Most studies in the past on ion-controlled lumines-
cent probes were focused on organic receptors that are based
(7) Whittall, I. R.; Humphrey, M. G.; Samoc, M.; Luther-Davies, B.
Angew. Chem., Int. Ed. 1997, 36, 370.
(8) (a) Rurack, K. Spectrochim. Acta, Part A 2001, 57, 2161. (b)
Barnham, K. J.; Masters, C. L.; Bush, A. L. Nat. Rev. Drug Discovery
2004, 3, 205. (c) Pontiki, E.; Hadjipavlou-Litina, D.; Chaviara, A. T.;
Bolos, C. A. Bioorg. Med. Chem. Lett. 2006, 16, 2234.
r
2009 American Chemical Society
Published on Web 05/19/2009
pubs.acs.org/Organometallics

3622 Organometallics, Vol. 28, No. 13, 2009
Communication
on polyaromatic luminophores.9,11 It was only quite recently
that metalloreceptors based on various transition metal
complexes, especially those that show metal-to-ligand charge
transfer (MLCT) excited state properties, have attracted
growing interest, with rhenium(I) and ruthenium(II) systems
being most extensively studied.12 To the best of our knowl-
edge, the employment of the intriguing photophysical prop-
erties of the gold(I) alkynyl complexes, with the advantages
of their simple, linear, and rigid structure, together with the
presence of a π-conjugated system, which is usually involved
in the origin of luminescence, in the design of luminescent
chemosensors is very rare. Very recently, we reported a
series of di- and tetranuclear gold(I) alkynylcrown and
alkynylcalixcrown complexes, which have been shown
to exhibit interesting photophysical and cation-binding
properties.4
Figure 1. Perspective drawing of complex 1 with atomic num-
bering scheme. Hydrogen atoms are omitted for clarity. Ther-
mal ellipsoids are shown at the 30% probability level.
Scheme 1. Schematic Representation of the Photophysical
Change of 1 upon Binding Cu2+
As an extension of our previous work in host-guest
chemistry, herein we report the synthesis of a novel lumines-
cent alkynylgold(I) complex, [PPh3AuCtCC6H4SO2N
(CH2-py-2)2] (1), with the dipicolyamine (DPA) receptor,
which is well-known to show remarkable binding ability to
transition metal ions and has been widely used in the design
of sensors for molecular recognition.9f,9g,13 The ion-binding
properties of the complex with various metal ions such as
Na+, K+, Mg2+, Ca2+, Ba2+, Cu2+, Zn2+, Cd2+, Hg2+
,
Pb2+, Fe3+, Fe2+, Co2+, and Ni2+ have been studied by
UV-vis and luminescence spectroscopy, and the complex
was found to be highly sensitive and selective toward Cu2+
ion, in which the luminescence is switched off upon Cu2+
binding. The recognition event was also found to show
(9) (a) Domaille, D. W.; Que, E. L.; Chang, C. J. Nat. Chem. Biol.
2008, 4, 168. (b) Zhang, X.; Shiraishi, Y.; Hirai, T. Org. Lett. 2007, 9,
5039. (c) Xu, Z.; Xiao, Y.; Qian, X.; Cui, J.; Cui, D. Org. Lett. 2005, 7,
889. (d) Pederson, C. J. J. Am. Chem. Soc. 1967, 89, 7017. (e) Minta, A.;
Kao, J. P.; Tsien, R. Y. J. Biol. Chem. 1989, 264, 8171. (f) Woodroofe, C.
C.; Lippard, S. J. J. Am. Chem. Soc. 2003, 125, 11458. (g) Woodroofe, C.
C.; Won, A. C.; Lippard, S. J. Inorg. Chem. 2005, 44, 3112.
(10) (a) Czarnik, A. W. In Fluorescent Chemosensors for Ion and
Molecule Recognition; American Chemical Society: Washington, DC,
1993. (b) De Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.;
Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem.
Rev. 1997, 97, 1515. (c) Pedersen, C. J. Angew. Chem., Int. Ed. 1988, 27,
1021. (d) Cram, D. J. Angew. Chem., Int. Ed. 1988, 27, 1009. (e) Lehn,
J. M. Angew. Chem., Int. Ed. 1988, 27, 89. (f) Beer, P. D.; Bayly, S. R.
Top. Curr. Chem. 2005, 255, 125.
complete reversibility, with the revival of the luminescence
signal upon addition of EDTA (Scheme 1).
Complex 1 was synthesized by reacting HCtCC6H4SO2N
(CH2-py-2)2 (HCtCC6H4SO2DPA) with
1 equiv of
PPh3AuCl in the presence of an excess of triethylamine in
dichloromethane. Subsequent layering of hexane onto a
dichloromethane solution of the complex gave the product
1
(11) (a) Fages, F.; Desvergne, J. P.; Bouas-Laurent, H.; Marsau, P.;
Lehn, J. M.; Kotzyba-Hibert, F.; Albrecht-Gary, A.; Al-Joubbeh, M. J.
Am. Chem. Soc. 1989, 111, 8672. (b) Fages, F.; Desvergne, J. P.;
Bouas-Laurent, H. J. Am. Chem. Soc. 1989, 111, 96.
as white crystals. The identity has been confirmed by H
NMR, 31P {1H} NMR, FAB-MS, and satisfactory elemental
analysis. The structure of the complex has also been deter-
mined by X-ray crystallography.
(12) (a) MacQueen, D. B.; Schanze, K. S. J. Am. Chem. Soc. 1991,
113, 6108. (b) Shen, Y.; Sullivan, B. P. Inorg. Chem. 1995, 34, 6235.
(c) Shen, Y.; Sullivan, B. P. J. Chem. Educ. 1997, 74, 685. (d) Sun, S. S.;
Lee, A. J.; Zavalij, P. Y. Inorg. Chem. 2003, 42, 3445. (e) Lewis, J. D.;
Moore, J. N. Dalton Trans. 2004, 1376. (f) Uppadine, L. H.; Redman,
J. E.; Dent, S. W.; Drew, M. G. B.; Beer, P. D. Inorg. Chem. 2001, 40,
2860. (g) Beer, P. D. Acc. Chem. Res. 1998, 31, 71. (h) Beer, P. D.; Dent,
S. W.; Wear, T. J. Chem. Soc., Dalton Trans. 1996, 2341. (i) Beer, P. D.;
Dent, S. W.; Hobbs, G. W.; Wear, T. J. Chem. Commun. 1997, 99. (j)
Harriman, A.; Hissler, M.; Jost, P.; Wipff, G.; Ziessel, R. J. Am. Chem.
Soc. 1999, 121, 14. (k) Rice, C. R.; Guerrero, A.; Bell, Z. R.; Paul, P. L.;
Motson, G. R.; Jeffery, J. C.; Ward, M. D. New J. Chem. 2001, 25, 185.
(l) Li, M. J.; Chu, B. W. K.; Yam, V. W. W. Chem.;Eur. J. 2006, 12,
3528. (m) Li, M. J.; Ko, C. C.; Duan, G. P.; Zhu, N.; Yam, V. W. W.
Organometallics 2007, 26, 6091. (n) Yam, V. W. W.; Lee, V. W. M. J.
Chem. Soc., Dalton Trans. 1997, 3005. (o) Yam, V. W. W.; Lee, V. W. M.
Inorg. Chem. 1997, 36, 2124. (p) Yam, V. W. W.; Wong, K. M. C.; Lee,
V. W. M.; Lo, K. K. W.; Cheung, K. K. Organometallics 1995, 14, 4034.
(13) (a) Wang, H. H.; Gan, Q.; Wang, X. J.; Xue, L.; Liu, S. H.; Jiang,
H. Org. Lett. 2007, 9, 4995. (b) Huang, S.; Clark, R. J.; Zhu, L. Org. Lett.
2007, 9, 4999. (c) Rhee, H. W.; Lee, C. R.; Cho, S. H.; Song, M. R.;
Cashel, M.; Choy, H. E.; Seok, Y. J.; Hong, J. I. J. Am. Soc. Chem. 2008,
130, 784.
The perspective drawing of the complex is shown in
˚
˚
Figure 1. The P-Au (2.274 A) and CtC (1.185 A) bond
lengths are comparable to those observed in other alkynyl-
gold(I) phosphine complexes.2-6 The P-Au-C angle of
174.9° is close to linear geometry and is typical of sp
hybridization found in Au(I) alkynyl complexes. The short-
˚
est intermolecular Au Au contact is 9.650 A, which
indicates the absence of Au Au interactions.
3 3 3
3 3 3
The photophysical data of complex 1 are tabulated in
Table 1. The UV-vis spectrum exhibits an intense high-
energy band at 270-302 nm, with a tail extending to ca. 400
nm. The close resemblance of the high-energy absorption
band to that observed in [Au(PPh3)Cl]5a and [Au(PPh3)
(CtCPh)]5a is suggestive of their similar origin and is tenta-
tively assigned as the intraligand transition characteristic of
triphenylphosphine. The low-energy tail that is absent in [Au
(PPh3)Cl] may be characteristic of the alkynylgold(I) com-

Communication
Table 1. Photophysical Data of Complex 1
Organometallics, Vol. 28, No. 13, 2009 3623
absorption
λ/nm(ε Â 10-4/dm3 mol-1 cm-1
emission
em/nm (τ0/μs)
)
medium (T/K)
λ
270 (2.72), 286 (3.00),
302 (3.35)
DCM (298)
444, 470 (0.20)
solid (298)
solid (77)
glass (77)a
468 (193)
468 (32.9)
447, 472 (26.0)
a In EtOH-MeOH-CH2Cl2 (4:1:1 v/v).
Figure 3. Job’s plot for the binding of complex 1 with Cu2+
showing 1:1 stiochiometry. The absorbance at 366 nm was
measured as a function of the molar ratio XM, where XM =
,
([Cu2+]/([Cu2+] + [1])).
Figure 2. UV-vis spectral changes of complex 1 (2.0 Â 10-5 M)
in CH2Cl2-MeOH (1:1 v/v; 0.1 M nBu4NPF6) upon addition of
Cu(ClO4)2. Inset: Plot of absorbance at 366 nm as a function of
Cu2+ concentration and its theoretical fit for the 1:1 binding of
complex 1 with Cu2+
.
plex. Excitation of 1 in CH2Cl2 and 77 K glass both gave a
structured emission band at ca. 444 and 472 nm with vibra-
tional progressional spacings of ca. 1336 cm-1, correspond-
.
ing to the C-C vibrational modes of the aromatic rings,
while the emission was centered at ca. 468 nm in the solid
state at both 298 and 77 K, typical of ligand-centered
emission. The absence of low-energy emission bands is
Figure 4. Emission spectral traces of 1 (2.0 Â 10-5 M) in
CH2Cl2-MeOH (1:1 v/v; 0.1 M nBu4NPF6) upon treatment of
Cu(ClO4)2. Excitation at the isosbestic wavelength of 286 nm.
Inset: Plot of emission intensity at 475 nm as a function of Cu2+
concentration and its theoretical fit for the 1:1 binding of
indicative of the absence of short Au Au contacts in the
3 3 3
solid states. The luminescence lifetimes in the microsecond
range are suggestive of an excited state of triplet parentage.
Addition of Cu2+ to a CH2Cl2-MeOH (1:1 v/v) solution
of 1 produced observable UV-vis spectral changes. A new
low-energy absorption band at 366 nm was formed, with a
well-defined isosbestic point at 286 nm, suggesting a clean
reaction that involved two absorbing species. Figure 2 shows
the electronic absorption spectral changes of 1 upon addition
of the Cu2+ ion in CH2Cl2-MeOH (1:1 v/v; 0.1 nBu4NPF6).
The new band at ca. 366 nm upon addition of Cu2+ is
tentatively assigned as the ligand-to-metal charge transfer
(LMCT), arising from the transfer of an electron from the
lone pair of the amine group to the metal-centered orbital. A
1:1 binding mode is proposed and confirmed by the method
of continuous variation.14 As can be seen from the Job’s
plot in Figure 3, a plot of absorbance at 366 nm versus XM
(= [Cu2+]/([Cu2+] + [1])) shows a break point at a molar
ratio of ca. 0.5, indicative of a 1:1 stoichiometry. A log Ks of
6.2 ( 0.1 of 1 for Cu2+ at 298 K was obtained from a
nonlinear least-squares fit for 1:1 binding. The inset of
complex 1 with Cu2+
.
Figure 2 shows a close agreement of the experimental data
to the theoretical fit, further supportive of the 1:1 binding.
When Cu2+ was added to the solution of 1, emission
quenching was observed, which is due to the energy or
electron transfer process because of the d9 electronic config-
uration. The stability constant was also determined from the
change of the emission intensity at 475 nm as a funcion of the
concentration of Cu2+ ion added using nonlinear least-
squares fit. A log Ks of 6.4 ( 0.1 was obtained, which is in
good agreement with that determined by the UV-vis spec-
trophotometric method. Figure 4 shows the changes in the
luminescence response of 1 toward Cu2+ in CH2Cl2-MeOH
n
(1:1 v/v; 0.1 M Bu4NPF6), excited at the isosbestic wave-
length of 286 nm. The inset of Figure 4 also shows a good
agreement of the experimental data to the theoretical fit
based on 1:1 binding stoichiometry.
The binding of Cu2+ to 1 was found to be reversible. When
an aqueous solution of EDTA disodium salt was added to a
solution of 1 (2.0 Â 10-5 M) and Cu2+ (4.0 Â 10-5 M) in
(14) (a) Jaffe, H. H.; Orchin, M. In Theory and Application of
UltraViolet Spectroscopy; Wiley: New York, 1962. (b) Rohwer, H.;
Collier, N.; Hoston, E. Anal. Chim. Acta 1995, 314, 219. (c) Peyman,
A.; Uhlmann, E.; Wagner, K.; Augustin, S.; Weiser, C.; Will, D. W.;
Breipohl, G. Angew. Chem., Int. Ed. 1997, 36, 2809. (d) Reddy, A. C. P.;
Sudharshan, E.; Rao, A. G. A.; Lokesh, B. R. Lipids 1999, 34, 1025.
n
CH2Cl2-MeOH (1:1 v/v; 0.1 M Bu4NPF6), the emission
intensity at 475 nm was completely revived and the absor-
bance at 366 nm in the UV-vis spectrum was found to

3624 Organometallics, Vol. 28, No. 13, 2009
Communication
Figure 5. Responses of 1 (2.0 Â 10-5 M) in CH2Cl2-MeOH
(1:1 v/v; 0.1 M nBu4NPF6) upon addition of 5 equiv of different
metal ions. Excitation was at 286 nm, and the emission was
monitored at 475 nm.
1
Figure 6. (a) H NMR spectral changes of 1 (5.86 mM) upon
addition of Zn(ClO4)2 in CDCl3-CD3OD (1:1 v/v). (b) Plot of
proton chemical shifts of NdCH (labled as b) as a function of
the concentration of Zn2+ added. (c) Job’s plots for 1:1 binding
of 1 with Zn2+ ions showing a 1:1 stoichiometry. The changes of
proton chemical shift of NdCH (labled as b) were followed,
where X1 = ([1]/([Zn2+] + [1])).
diminish, suggesting that Cu2+ has been extracted out of the
DPA unit, confirming the complete reversibility of the Cu2+
binding process.
To examine the selectivity of complex 1 toward various
metal ions, the luminescence response upon addition of
complexation of zinc ions to the DPA moiety, a decrease in
the electron density on the DPA unit and the conjugated
phenyl ring would cause a downfield shift of the signal. The
experimental data were found to be in good agreement with
the theoretical fit obtained from the EQNMR program using
a 1:1 binding model.17 The binding constant log Ks for Zn2+
was determined to be 2.20 ( 0.05, which is much smaller than
metal ions such as Na+, K+, Mg2+, Ca2+, Ba2+, Cu2+
,
Zn2+, Cd2+, Hg2+, Pb2+, Fe3+, Fe2+, Co2+, and Ni2+ has
been investigated. As shown in Figure 5, a drastic spectral
change is shown by Cu2+ binding, indicating the high
selectivity of 1 toward Cu .
2+ 15 While Hg2+ shows a similar
phenomenon of emission quenching, the change is to a lesser
extent. For all other metal ions, including some transition
that for Cu2+, suggesting the higher selectivity for Cu2+
.
In addition, the 1:1 stiochiometry between 1 and Zn2+
was further confirmed by the Job’s method of continuous
variation.
In summary, a novel DPA-containing alkynylgold(I) com-
plex has been successfully synthesized and structurally char-
acterized. The complex has been shown to exhibit a rich
photoluminescence property and to function as a selective
sensor for Cu2+, as revealed by the large UV-vis change and
significant emission quenching.
metal ions that have a partially filled d-orbital, such as Co2+
,
Ni2+, and Fe2+, very small to negligible changes were
observed under identical conditions. However, addition of
Fe3+ would cause a modest increase of the emission intensity
by ca. 1.4-fold. The reason has been ascribed to the
increased acidity as a result of the strong hydrolyzing ability
of Fe .
3+ 16 Although DPA is also well-known to readily bind
Zn2+ ion, no spectral changes were observed upon addition
of Zn2+ ions, probably due to the lack of a quenching
pathway.
Acknowledgment. V.W.-W.Y. acknowledges the sup-
port from The University of Hong Kong under the
Distinguished Research Achievement Award Scheme
and the URC Strategic Research Theme on Molecular
Materials. This work has been supported by a General
Research Fund (GRF) grant from the Research Grants
Council of Hong Kong Special Administrative Region,
P. R. China (HKU 7050/08P). X.H. acknowledges the
receipt of a postgraduate studentship, administered by
The University of Hong Kong.
Since Cu2+ is a paramagnetic metal ion, not suitable for
the NMR experiment, the 1H NMR titration study of 1 with
Zn2+ was carried out instead (Figure 6). The 1H NMR
titration experiment in CDCl3-CD3OD (1:1 v/v) showed
that the proton resonances on the pyridine and phenyl rings
were shifted downfield and became broader upon Zn2+
addition, indicating the coordination of Zn2+ ion to 1. Upon
(15) A competitive ion-binding experiment was also studied. Addi-
tion of Cu2+ (1.0 Â 10-4 M) to a CH2Cl2-MeOH (1:1 v/v) solution of 1
(1.9 Â 10-5 M) containing an excess of Na+, K+, Mg2+, Ca2+, Ba2+
,
Cu2+, Zn2+, Cd2+, Pb2+, Fe3+, Fe2+, Co2+, and Ni2+ (ca. 1.0 Â 10-4
M, respectively) led to immediate quenching of the emission intensity
(though the emission change is only about half that in the absence of
other metal ions), suggesting that Cu2+ could displace other metal ions
from binding with complex 1.
Supporting Information Available: Synthesis and chara
cterization of the ligand and complex 1 and the X-ray
crystallographic determination data of 1. This material is
available free of charge via the Internet at http://pubs.
acs.org.
(16) This has been verified by performing the measurements under
buffered conditions in HEPES buffer (pH 7.2), where quenching of the
emission intensity was observed but to a much lesser extent than that of
Cu2+ under the same buffered conditions.
(17) Hynes, M. J. J. Chem. Soc., Dalton Trans. 1993, 311.