Zn2+-selective fluorescent turn-on chemosensor based on terpyridine-substituted siloles

Article abstract of DOI:10.1016/j.dyepig.2012.04.007

Two terpyridine-containing siloles (1 and 2) have been synthesized and their optical and metal sensing properties have been investigated in this work. 1 and 2 display a high selectivity for Zn²⁺ in comparison with alkali and alkaline earth meta

Full text of DOI:10.1016/j.dyepig.2012.04.007

Dyes and Pigments 95 (2012) 174e179
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Zn2þ-selective fluorescent turn-on chemosensor based on
terpyridine-substituted siloles
,
b
,
c
Shouchun Yin a, Jing Zhang a, Haike Feng a, Zujin Zhao a, Liwen Xu b, Huayu Qiu a , Benzhong Tang
*
a College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036, China
b Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, China
c Department of Chemistry and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two terpyridine-containing siloles (1 and 2) have been synthesized and their optical and metal sensing
properties have been investigated in this work. 1 and 2 display a high selectivity for Zn2þ in comparison
Received 15 March 2012
Received in revised form
16 April 2012
Accepted 17 April 2012
Available online 25 April 2012
with alkali and alkaline earth metal ions (Naþ, Kþ, Mg2þ, Ca2þ) and other transition metal ions (Ba2þ
,
Zn2þ, Fe2þ, Pb2þ, Ni2þ, Co2þ, Hg2þ, Agþ) upon excitation at 380 nm in THF. As being chemosensor, 1 with
two terpyridine groups at both ends shows better Zn2þ sensing properties than 2 containing only one
terpyridine group at end due to the formation of a metaleorganic coordination oligomer or polymer.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Siloles
Terpyridine
Fluorescent sensor
Zinc (II)
Aggregation-induced emission
Spectroscopic properties
1. Introduction
with the p* orbital of the butadiene fragment [12,13]. Siloles also
show intriguing aggregation-induced emission (AIE) characteristic,
first reported by Tang and co-workers [14]. Propeller-like silole
molecules are almost nonluminescent in solutions but become
highly emissive when aggregated in poor solvents or in solid state.
Therefore, due to the excellent photophysical and electronic
properties, siloles have been widely used as organic electrolumi-
nescent devices, organic solar cells, and chemosensors for explosive
detection and ion monitoring [15e29].
It is well known that terpyridine has a strong and directed metal
coordination capacity [30]. We connected the terpyridine moiety
covalently with the silole core in order to endow silole with metal
chelating properties. Here, we report the synthesis and character-
ization of two terpyridine end-capped siloles, 1,1-dimethyl-3,4-
diphenyl-2,5-bis(40-biphenyl-2,20:60,200-terpyridine) silole (1) and
1,1-dimethyl-3,4-diphenyl-2-(4-biphenyl-2,20:60,200-terpyridine)-
5-(p-bromophenyl) silole (2). Their photophysical properties and
potential applications as metal ion sensors have been investigated.
1 and 2 display a high selectivity for Zn2þ in comparison with all
other test metal ions upon excitation at 380 nm in THF. As being
chemosensor, 1 with two terpyridine groups at both ends shows
better Zn2þ sensing properties than 2 containing one terpyridine
group due to the formation of metaleorganic coordination olig-
omer or polymer.
In the past decade, the development of fluorescent chemo-
sensors with high selectivity and sensitivity has been a great
interest field in supramolecular chemistry [1]. Zn2þ is the second
most abundant transition metal ion in the human system after iron,
which plays an important role in various biological processes, such
as enzyme regulation, gene expression, neural signal transduction
and protein synthesis [2,3,4]. However, if unregulated, Zn2þ can
cause many severe diseases, such as Alzheimer’s disease, Parkin-
son’s disease, amyotrophic lateral sclerosis, hypoxiaeischemia and
epilepsy [5,6,7]. Meanwhile, excessive Zn2þ makes water smelly
and muddy, which is harmful to the environment [8]. Thus, the
development of an efficient Zn2þ-selective fluorescent sensor is
important for the fundamental research and biological application
[9,10,11].
Siloles are a class of particularly interesting molecules that
possess low-lying LUMO levels and high electron affinity arising
from the orbital interaction of the s* orbital of the silylene moiety
* Corresponding author. College of Material, Chemistry and Chemical Engi-
neering, Hangzhou Normal University, Hangzhou 310036, China. Tel.: þ86 571
28867898; fax: þ86 571 28867899.
E-mail address: huayuqiu@gmail.com (H. Qiu).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2012.04.007

S. Yin et al. / Dyes and Pigments 95 (2012) 174e179
175
2. Experimental
2.3.3. 1,1-Dimethyl-3,4-diphenyl-2,5-bis(40-biphenyl-2,20:60,200-
terpyridine) silole (1)
2.1. Materials
570 mg (1.0 mmol) 1,1-dimethyl-3,4-diphenyl-2,5-bis(4-bromo-
phenyl)silole (4), 435 mg (1.0 mmol) 5 and 138 mg K2CO3
(1.0 mmol) were dissolved in 25 mL of THF and 5 mL of H2O under
argon. To this solution 115 mg (0.1 mmol) Pd(PPh3)4 were added.
The reaction mixture was refluxed for 72 h. After cooling to room
temperature, the precipitate was filtered, and dissolved in excess
amount of CH2Cl2 (500 mL). The solution was then washed with
aqueous KOH solution (2%) and water. The organic layer was
separated and dried over MgSO4. After filtration, the solvent was
evaporated under reduced pressure to give yellow solid 1 (180 mg,
1,1-Dimethyl-3,4-diphenyl-2,5-bis(4-bromophenyl)silole
was
synthesized according to literature procedures [31]. 4-Bromo-
benzaldehyde, 2-acetylpyridine, 3,4-dimethoxyphenylboronic acid,
bis(pinacolato)diboron, dry dimethyl sulfoxide (DMSO), [1,10-bis(di-
phenylphosphino)ferrocene]dichloropalladium(II)
[Pd(dppf)Cl2],
and tetrakis(triphenylphosphine)palladium(0) [Pd(PPh3)4] were
purchased from Acros and used without further purification. Tetra-
hydrofuran (THF) was distilled from sodium prior to use. The metal
salts [AgClO4, Ba(ClO4)2, Ca(ClO4)2, Co(ClO4)2, Cu(ClO4)2$6H2O,
FeCl2$4H2O, Hg(ClO4)2, KClO4, Mg(ClO4)2 NaClO4, Ni(ClO4)2$6H2O,
Pb(ClO4)2$3H2O and Zn(ClO4)2] were purchased from Aldrich.
35% yield). M. p. ¼ 335e339 ꢀC. 1H NMR (400 MHz, CDCl3)
d (ppm):
8.76 (s, 4H), 8.72 (d, 4H), 8.66 (d, J ¼ 8.0 Hz, 4H), 7.95 (d, J ¼ 8.0 Hz,
4H), 7.85 (d, J ¼ 6.8 Hz, 4H), 7.69 (d, J ¼ 8.0 Hz, 5H), 7.47 (d,
J ¼ 7.6 Hz, 4H), 7.32 (d, J ¼ 5.2 Hz, 5H), 7.25 (m, 2H), 7.08 (m, 4H),
6.92 (m, 4H), 0.59 (s, 6H). 13C NMR (100 MHz, CDCl3)
d (ppm): 156.1,
2.2. Instrumentation
155.8, 154.6, 154.0, 150.0, 149.0, 141.3, 141.2, 140.5, 138.9, 138.7,
138.6, 138.3, 137.2, 136.8, 131.0, 130.3, 129.8, 129.3, 127.5, 127.1,
126.5, 126.4, 123.8, 121.3, 119.4, 118.5, ꢂ3.8. MALDI-TOF MS: calcd.
for C72H52N6Si 1029.4098, found 1029.4095.
1H and 13C NMR spectra were recorded at room temperature
on a Bruker Avance 400 operating at a frequency of 400 MHz
for 1H and 100 MHz for 13C. Melting points were taken on
a Beijing Taike X-5 melting point instrument. Mass spectra were
recorded on a Hewlett-Packard 5989 A mass spectrometer (ESI
mode) and Bruker Daltonics’ micrOTOF-Q II 10324 (MALDI-TOF
MS).
UVevis absorption spectra were recorded on a Perkin Elmer
Lambda 40 UVevis spectrophotometer. Corrected steady-state
excitation and emission spectra were obtained using a HITACHI
F-2700 Fluorescence Spectrophotometer. Relative quantum yields
were obtained by comparing the areas under the corrected
emission spectra of sample and fluorescence standard. Coumarin I
in ethanol (lex ¼ 380 nm, Ff ¼ 0.64) was used as fluorescence
standard. All spectra were recorded at 25 ꢀC using undegassed
samples.
2.3.4. 1,1-Dimethyl-3,4-diphenyl-2-(4-biphenyl-2,20:60,200-
terpyridine)-5-(p-bromophenyl) silole (3)
This compound was synthesized by analogous procedures
described for 1, from 285 mg (0.5 mmol) 4, 218 mg (0.5 mmol) 5,
69 mg K2CO3 (0.5 mmol), and 58 mg (0.05 mmol) Pd(PPh3)4.
Purification was performed by chromatography on silica gel with
a mixture of petroleum ether and ethyl acetate (4:1, v/v) to give
a yellow solid (228 mg, 57% yield). M. p. ¼ 292e296 ꢀC. 1H NMR
(400 MHz, CDCl3)
d
(ppm): 8.78 (s, 2H), 8.74 (d, J ¼ 4.0 Hz, 2H), 8.69
(d, J ¼ 8.0 Hz, 2H), 7.96 (d, J ¼ 8.4 Hz, 2H), 7.89 (m, 2H), 7.70 (d,
J ¼ 8.4 Hz, 2H), 7.46 (d, J ¼ 8.4 Hz, 2H), 7.36 (t, J ¼ 6.8 Hz, 2H), 7.25
(d, J ¼ 8.0 Hz, 2H), 7.04 (m, 8H), 6.86 (m, 2H), 6.80 (d, J ¼ 8.0 Hz, 4H),
0.52 (s, 6H). ESI-MS: m/z 800.55 [M þ H]þ.
2.3. Synthesis
2.3.5. 1,1-Dimethyl-3,4-diphenyl-2-(4-biphenyl-2,20:60,200-
terpyridine)-5-(p-bromophenyl) silole (2)
2.3.1. 40-(p-Bromophenyl)-2,20:60,200-terpyridine (6)
This compound was synthesized by analogous procedures
described for 1, from 200 mg (0.25 mmol) 3, 91 mg (0.5 mmol) 3,4-
dimethoxyphenylboronic acid, 35 mg K2CO3 (0.25 mmol), and
29 mg (0.025 mmol) Pd(PPh3)4. Purification was performed by
chromatography on silica gel with a mixture of petroleum ether
and ethyl acetate (4:1, v/v) to give a yellow solid (139 mg, 65%
To 4-bromobenzaldehyde (1.0 g, 5.40 mmol) in 120 mL CH3OH
was added 2-acetylpyridine (1.3 g, 10.80 mmol), NaOH (0.22 g,
5.4 mmol) and 30 mL concentrated NH4OH. The reaction mixture
was refluxed for 72 h, and then stirred at room temperature for
another 3 h. The formed slight yellow precipitate was filtered and
washed sequentially with H2O and CH3OH. White powder could be
obtained after recrystallization from EtOH (1.8 g, 88% yield). M.
yield). M. p. ¼ 315e318 ꢀC. 1H NMR (400 MHz, CDCl3)
d (ppm): 8.83
(s, 2H), 8.77 (d, J ¼ 4.4 Hz, 2H), 8.72 (d, J ¼ 7.6 Hz, 2H), 8.01 (d,
J ¼ 8.0 Hz, 2H), 7.94 (t, J ¼ 7.6 Hz, 2H), 7.72 (d, J ¼ 8.0 Hz, 2H), 7.47 (d,
J ¼ 8.4 Hz, 2H), 7.40 (t, J ¼ 6.0 Hz, 2H), 7.35 (d, J ¼ 8.4 Hz, 2H), 7.26
(m, 3H), 7.06 (m, 8H), 7.01 (d, J ¼ 8.4 Hz, 2H), 6.80 (m, 4H), 3.93 (s,
3H), 3.91 (s, 3H), 0.57 (s, 6H). ESI-MS: m/z 858.55 [M þ H]þ.
p. ¼ 155e157 ꢀC. 1H NMR (400 MHz, CDCl3)
d (ppm): 8.71 (d,
J ¼ 4.2 Hz, 2H), 8.66 (s, 2H), 8.63 (d, J ¼ 8.6 Hz, 2H), 7.86 (m, 2H),
7.75 (d, J ¼ 8.6 Hz, 2H), 7.61 (d, J ¼ 8.6 Hz, 2H), 7.35 (m, 2H). 13C NMR
(100 MHz, CDCl3)
d (ppm): 156.0, 149.1, 149.0, 137.4, 136.9, 132.1,
128.9, 123.9, 123.4, 121.3, 118.5.
3. Results and discussion
2.3.2. 40-(p-Pinacolatoboronphenyl)-2,20:60,200-terpyridine (5)
774 mg 6 (2 mmol), 533 mg bis(pinacolato)diboron (2.1 mmol),
50 mg Pd(dppf)Cl2 (0.06 mmol) and 402 mg KOAc (6 mmol) were
added into 5 mL of dry and degassed DMSO, and then flushed with
nitrogen. The mixture was stirred at 80 ꢀC for 6 h under nitrogen.
Then 50 mL of toluene was added and washed with water
(3 ꢁ 150 mL) to remove DMSO from the toluene layer. The toluene
layer was dried over MgSO4 and the solvent was evaporated under
reduced pressure to give a white solid (348 mg, 40% yield). M.
3.1. Synthesis
Silole derivate 1 with two terpyridine functional groups at both
ends (1,1-dimethyl-3,4-diphenyl-2,5-bis(40-biphenyl-2,20:60,200-ter-
pyridine) silole) was synthesized according to the synthetic route
shown in Scheme 1. In the presence of NaOH and concentrated
NH4OH, 4-bromobenzaldehyde was reacted with 2-acetylpyridine
to get 6. By Miyaura coupling reaction the bromo group of 6 was
transferred into pinacolatoboron group at the presence of
Pd(dppf)2Cl2 as catalyst. The Suzuki coupling of 4 and 5 with
Pd(PPh3)4 as catalyst afforded ditopic ligand 1 and 3 in moderate
yields of 35% and 57%, respectively. Although we can obtain 1 and 3
p. ¼ 187e194 ꢀC. 1H NMR (400 MHz, CDCl3)
d (ppm): 8.76 (s, 2H),
8.75 (d, J ¼ 4.8 Hz, 2H), 8.65 (d, J ¼ 7.9 Hz, 2H), 7.97 (d, J ¼ 8.4 Hz,
2H), 7.94 (d, J ¼ 8.4 Hz, 2H), 7.87 (d, J ¼ 7.9 Hz, 2H), 7.35 (m, 2H),1.38
(s, 6H).

176
S. Yin et al. / Dyes and Pigments 95 (2012) 174e179
O
O
O
O
O
O
B
B
N
N
N
N
NaOH, MeOH
NH4OH
O
O
Br
N
+
N
B
N
Pd(dppf)Cl2, KOAc, DMSO
Br
6
5
Br
Br
5
1) LiNaph, THF
ClZn
ZnCl
Br
Br
Pd(PPh3)4
K2CO3
Si
2) ZnCl2-TMEDA
Si
Si
Pd(PPh3)2Cl2
THF, H2O
4
7
8
N
N
N
N
Si
N
N
1
Scheme 1. Synthetic route to 1.
simultaneously by one-pot Suzuki coupling reaction of 4 and 5, the
separation of the products is very difficult and cumbersome, and it
is not easy to get the compounds pure enough for NMR spectro-
scopic characterization. Here, an excess amount of 4 was used and
the reaction time was elongated to make sure that 5 was reacted
completely during the synthetic procedure of 1, which facilitates
the separation of the desired products. On the other hand, an equal
equivalent of 4 and 5 in a short reaction time yields intermediate 3
that reacts with 3,4-dimethoxyphenylboronic acid to afford 2 for
comparison (Scheme 2). The reaction intermediates and final
products were fully characterized by NMR and Mass spectroscopy
and satisfactory data corresponding to their structures are
obtained. 1 and 2 are soluble in THF, CH3CN and DMSO, and slightly
soluble in C2H5OH and CH3OH.
photophysical properties of 1 upon addition of several metal
cations (Naþ, Kþ, Mg2þ, Ca2þ, Ba2þ, Cu2þ, Zn2þ, Fe2þ, Pb2þ, Ni2þ
,
Co2þ, Hg2þ, Agþ) in THF were investigated by fluorescence spec-
troscopic measurements and titration studies. Fig. 1 shows the
fluorescence response of 1 (1.0 ꢁ 10ꢂ4 mol/L) to the above
mentioned metal cations (1 equiv) measured in THF upon excita-
tion at lex ¼ 380 nm. A THF solution of free 1 shows weak fluo-
rescence peaked at w500 nm but the intensity is very weak due to
the intramolecular rotations of the phenyl rings linked to silole core
[25]. In the presence of Naþ, Kþ, Mg2þ, Ca2þ and Ba2þ, the fluo-
rescence intensity and the spectral pattern of 1 show no obvious
changes. Addition of Cu2þ, Fe2þ, Pb2þ, Ni2þ, Co2þ and Hg2þ to free 1
quenches the light emission, accompanied by a red-shift of
w10 nm. The emission maximum of free 1 further moves to
526 nm, but the emission intensity changes slightly when Agþ ions
are added. Agþ can induce the enhancement of the fluorescence
3.2. Spectral characteristics
intensity, instead of quenching, by 15% compared with Cu2þ, Fe2þ
,
As terpyridine is a well-known metal chelating unit, we
wondered if 1 can be used as a chemosensor for metal ions. The
Pb2þ, Ni2þ, Co2þ, Hg2þ. Interestingly, when Zn2þ ions are added to 1
in THF solution, the fluorescence spectrum of the complex shows
Scheme 2. Synthetic route to 2.

S. Yin et al. / Dyes and Pigments 95 (2012) 174e179
177
1 upon coordination with Zn2þ may be due to the formation of
metaleorganic coordination polymers or oligomers, where the
entangled molecular chains restrict the intramolecular rotation of
the silole core to some extent, and thus reduce the nonradiative
energy decay. Comparing the structure of 1 with 2, it can be seen
that 1 contains two terpyridine groups at both ends, while 2 has
only one terpyridine group at end. Thus, 2 cannot form polymers or
oligomers but a 2:1 complex with Zn2þ. Direct evidence for the
formation of metaleorganic coordination oligomers or polymers
was obtained from the results of 1H NMR. As shown in Fig. 3, the
absorption of the aryl protons of 1 becomes broadened and the
1500
1200
900
600
300
0
1
Ag+
Ba2+
Ca2+
Co2+
Cu2+
Fe2+
Hg2+
K+
Mg2+
Na+
Ni2+
Pb2+
Zn2+
characteristic absorption of terpyridine protons at d 8.76, 8.72, 8.66,
7.47 ppm shifts to a lower field after the coordination of 1 with
Zn2þ. The formed oligomer or polymer has lower solubility in THF
solution and accordingly form aggregates to result in the
enhancement of the fluorescence from the silole core in 1 due to the
AIE characteristics of the silole core [25]. The formed dimmer can
be soluble in THF, so the fluorescence intensity does not increase.
This is may be the reason that the fluorescence intensity is greatly
enhanced when Zn2þ is coordinated with 1, not 2. To prove this
hypothesis, we added water (poor solvent) into the THF solution of
2 and Zn2þ. After addition of water, the fluorescence intensity the
complex of 2 and Zn2þ is increased. Because 1 displays better
properties as chemosensor than 2, we will focus our investigation
on the metal sensing properties of 1 in the following discussion.
The fluorescence titration of 1 in the presence of different Zn2þ
concentrations was then performed. As shown in Fig. 4, 1 emits
weak fluorescence at w500 nm. After addition of Zn2þ into the THF
solution, the emission spectra gradually red-shift and the fluores-
cence intensity increases significantly with the increase of the
concentration of Zn2þ when excited at 380 nm. The fluorescence
quantum yield increases from 0.05 for free 1 to 0.27 for the complex
of 1 and Zn2þ, correspondingly. The dependence of the emission
intensity at 522 nm on the concentration of Zn2þ is shown in the
inset of Fig. 4. As depicted in the inset of Fig. 4, the fluorescence
intensity at 522 nm increases almost linearly with the increase of
the concentration of Zn2þ in the range of 1.0 equiv of Zn2þ, which
facilitates the quantitative analysis of Zn2þ in THF.
400
450
500
550
600
650
700
Wavelength / nm
Fig. 1. Fluorescence emission spectra of 1 (1.0 ꢁ 10ꢂ4 mol/L) upon addition of various
metal ions (1 equiv) in THF (lex ¼ 380 nm).
a significant bathochromic shift and the fluorescence intensity
exhibits a great enhancement. Chemosensors showing fluorescence
enhancement due to metaleion binding are more sensitive than
those exhibiting fluorescence quenching. These observations indi-
cate that 1 can be used as a turn-on chemosensor for Zn2þ
.
The emission spectra of 2 upon exposure to the above test metal
ions are shown in Fig. 2. Similar to 1, Naþ, Kþ, Mg2þ, Ca2þ and Ba2þ
exert no effect on the fluorescence of 2 because terpyridine does
not coordinate with the above metal ions, and Cu2þ, Fe2þ, Pb2þ
,
Ni2þ, Co2þ and Hg2þ can efficiently quench the emission of free 2.
Unlike 1, in the presence of Agþ, the spectral pattern keeps
unchanged but the fluorescence intensity becomes a little weaker.
Zn2þ can also shift the emission spectrum of 2 bathochromically
but the fluorescence intensity has almost no enhancement.
The red-shifts of 1 and 2 upon coordination with Zn2þ may be
due to intramolecular charge transfer (ICT) effect. Compared to the
silole core terpyridine has stronger electron-withdrawing capa-
bility. The coordination of 1 or 2 with Zn2þ intensifies the electron-
withdrawing character of terpyridine, facilitating the occurrence of
the ICT process. Thus, the emission of 1 shifts to the longer wave-
lengths [32] when Zn2þ is added. The greatly enhanced emission of
To determine the binding stoichiometry of 1 and Zn2þ, Job’s
method for the emission is employed. The concentrations of 1 and
Zn2þ are varied, while the sum of the two concentrations is kept
constant at 2.0 ꢁ 10ꢂ4 mol/L. The change of the fluorescence
intensity at 522 nm with the concentration ratio of 1 to Zn2þ is
300
2
Ag+
1 and Zn2+
Ba2+
Ca2+
Co2+
Cu2+
Fe2+
Hg2+
K+
250
200
150
100
50
Mg2+
Na+
1
Ni2+
Pb2+
Zn2+
0
400
450
500
550
600
650
700
9.5
9.0
8.5
8.0
7.5
7.0
6.5
Wavelength / nm
ppm
Fig. 2. Fluorescence emission spectra of 2 (1.0 ꢁ 10ꢂ4 mol/L) upon addition of various
metal ions (1 equiv) in THF (lex ¼ 380 nm).
Fig. 3. 1H NMR spectra of 1 and the complex of 1 and Zn2þ in chloroform-d.

178
S. Yin et al. / Dyes and Pigments 95 (2012) 174e179
1500
1200
900
600
300
0
100 μΜ
0 μΜ
400
450
500
550
600
650
700
Wavelength / nm
Fig. 6. The relative fluorescence intensity of 1 (1.0 ꢁ 10ꢂ4 mol/L) containing 1.0 equiv
of Zn2þ to the selected metal ions (2.0 equiv). F1þZn and F1þZnþM denote the fluores-
cence signals of 1 in the presence of Zn2þ only and in the presence of Zn2þ as well as
the competing ions, respectively. Excitation was at 380 nm and emission was at
522 nm.
Fig. 4. Fluorescent emission spectra of 1 (1.0 ꢁ 10ꢂ4 mol/L) upon excitation at 380 nm
in the presence of different concentrations of Zn2þ (0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35,
0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0 equiv) in THF. Inset:
Fluorescence emission intensity of 1 (1.0 ꢁ 10ꢂ4 mol/L) in THF monitored at 522 nm as
a function of Zn2þ concentration.
of 1 with Zn2þ was partly quenched, while Cu2þ can almost quench
the fluorescence emission of the coordination of 1 with Zn2þ due to
shown in Fig. 5. When the molecular fraction of Zn2þ is closed to
50%, the complex of 1 and Zn2þ exhibited a maximum fluorescence
emission at 522 nm. This indicates that a 1:1 stoichiometry is
possible for the binding mode of 1 and Zn2þ, which is consistent
with the binding mode of terpyridine to Zn2þ reported in the
literature [30,32].
the paramagnetic properties of Cu2þ
.
4. Conclusions
In conclusion, in this work, two terpyridine-containing silole
derivatives are synthesized and characterized. The silole derivative
1 with two terpyridine groups can sensitively and selectively detect
Zn2þ in THF. When Zn2þ is added, 1 displays a strong red-shift and
a remarkable enhancement of the fluorescence intensity. Thus 1
can be used as a turn-on chemosensor for Zn2þ. The future work
will focus on the utility of 1 for zinc imaging in live cells.
3.3. Selectivity and tolerance of 1 to Zn2þ over other metal ions
The selectivity and tolerance of 1 to Zn2þ over other metal ions
are investigated by measuring the fluorescence response of 1 with
Zn2þ in the presence of other competitive metal ions. 2.0 Equiv of
above mentioned metal ions (2.0 ꢁ 10ꢂ4 mol/L) was added to 1.0
equiv of the complex of 1 and Zn2þ in THF and the fluorescence
response (I522) was detected and then compared with that of 1 in
THF containing only 1.0 equiv of Zn2þ. As shown in Fig. 6, Naþ, Kþ,
Mg2þ, Ca2þ and Ba2þ exhibit only a small or no interference with
Acknowledgements
We thank National Natural Science Foundation of China (No.
21074028, 91127032, 21174035, 21104012), Zhejiang Provincial
Natural Science Foundation of China (No. Y4100287, Y4110331),
Program for Excellent Young Teachers in Hangzhou Normal
University (No. HNUEYT 2011-01-019), and the Opening Founda-
tion of Zhejing Provincial Top Key Discipline (No. 20110943) for
financial supports.
the affinity of 1 and Zn2þ. However, in the presence of Fe2þ, Pb2þ
,
Ni2þ, Co2þ and Hg2þ the fluorescence emission of the coordination
1500
1200
900
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