Ratiometric and selective fluorescent sensor for Zn2+ as an "off-on-off" switch and logic gate

Article abstract of DOI:10.1021/ic300738e

A new chemosensor, 2,3,15,16-tetrakis(pyridin-2-yl)-7,8,10,11,20,21,23,24- octahydro[1,4,7,10,13,16]hexaoxacyclooctadecino[2,3-g:11,12-g′] diquinoxaline (1), containing 2,3-bis(pyridin-2-yl)quinoxaline and crown ether moieties, has been designed and found to be a ratiometric and selective fluorescent detector of Zn²⁺ over a wide range of tested metal ions. The addition of Zn²⁺ to the solution of 1 in acetonitrile induced the formation of a 1:2 ligand-metal complex, 1-Zn²⁺, which exhibits a remarkable enhanced fluorescent emission centered at 460 nm, with the disappearance of the fluorescent emission of 1 centered at 396 nm due to the mechanism of internal charge transfer. In contrast, the presence of K ⁺ results in the fluorescence quenching of 1 and 1-Zn²⁺ through the photoinduced electron-transfer mechanism. These results demonstrate that 1 can perform as not only an INHIBIT logic gate but also an "off-on-off" molecular switch triggered by Zn²⁺ and K ⁺. The structure of complex 1-Zn²⁺ has been characterized by single-crystal X-ray crystallography, mass spectrometry, and ¹H NMR titration experiments. Density functional theory calculation results on 1 and the 1-Zn²⁺ complex are well consistent with the experimental results.

Full text of DOI:10.1021/ic300738e

Article
pubs.acs.org/IC
2+
Ratiometric and Selective Fluorescent Sensor for Zn as an “Off−
On−Off” Switch and Logic Gate
Ya-Ping Li, Hua-Rong Yang, Qiang Zhao, Wei-Chao Song, Jie Han, and Xian-He Bu*
Tianjin Key Lab on Metal and Molecule-based Material Chemistry, Department of Chemistry, Nankai University, Tianjin 300071,
China
*
S Supporting Information
ABSTRACT: A new chemosensor, 2,3,15,16-tetrakis(pyridin-
-yl)-7,8,10,11,20,21,23,24-octahydro[1,4,7,10,13,16]-
2
hexaoxacyclooctadecino[2,3-g:11,12-g′]diquinoxaline (1), con-
taining 2,3-bis(pyridin-2-yl)quinoxaline and crown ether
moieties, has been designed and found to be a ratiometric
2
+
and selective fluorescent detector of Zn over a wide range of
2
+
tested metal ions. The addition of Zn to the solution of 1 in
acetonitrile induced the formation of a 1:2 ligand−metal
2
+
complex, 1-Zn , which exhibits a remarkable enhanced
fluorescent emission centered at 460 nm, with the disappear-
ance of the fluorescent emission of 1 centered at 396 nm due to
the mechanism of internal charge transfer. In contrast, the
+
presence of K results in the fluorescence quenching of 1 and 1-
2+
Zn through the photoinduced electron-transfer mechanism.
These results demonstrate that 1 can perform as not only an
INHIBIT logic gate but also an “off−on−off” molecular switch
2
+
+
2+
triggered by Zn and K . The structure of complex 1-Zn has
1
been characterized by single-crystal X-ray crystallography, mass spectrometry, and H NMR titration experiments. Density
functional theory calculation results on 1 and the 1-Zn2+ complex are well consistent with the experimental results.
INTRODUCTION
and interesting to seek a fluorescent sensor to construct logic
gates and switches with Zn2+ and K .
Until now, di-2-picolylamine, cyclic polyamines, and acyclic
■
+
Recently, much attention has been focused on the development
of a ratiometric and fluorescent probe for zinc ions in
supramolecular chemistry. As is well-known, Zn plays an
important role in the human body and in biological activities
such as structural and catalytic cofactors, neural signal
1
2+
iminodiacetic acid, bipyridine, quinoline, and Schiff bases have
been used as Zn2+ chelators;
3j,9
they all have a defined
2+
coordination pattern and show strong affinities to Zn . In
contrast, crown ether units have been proven to exhibit
excellent binding ability with alkali metals; among many kinds
of crown ethers, [2,4]dibenzo-18-crown-6 derivatives and
calixcrowns have great preference for K ions.
we present a new fluorophore, 2,3,15,16-tetrakis(pyridin-2-yl)-
,8,10,11,20,21,23,24-octahydro[1,4,7,10,13,16]-
2
transmitters, or modulators. The development of highly
selective and ratiometric fluorescent chemosensors for Zn
2
+
3
ions is still an important task, although some fluorescent
+
8,10,11
Herein,
sensors for Zn2 by the ratio of the emission intensity changes
+
3
a,j−n
at two wavelengths have been reported in the literature.
7
Especially, ratiometric fluorescent probes are more favored by
the researchers because a ratiometric read-out eliminates the
environmental influence on the fluorescence intensity.
hexaoxacyclooctadecino[2,3-g:11,12-g′]diquinoxaline (1),
which consists of two different binding moieties [2,3-
bis(pyridin-2-yl)quinoxaline and [2,4]dibenzo-18-crown-6].
2,3-Bis(pyridin-2-yl)quinoxaline was chosen as a building
A number of fluorescent sensors/probes have been reported
4
,5
2+
2+
as molecular logic gates. In general, the reported systems
were devised by modulation of the emission properties of the
sensors by different combinations of heavy-metal ions, such as
block because of its affinity for Zn and/or Cd ions as well
as its excellent optical properties and extensive application in
12
molecular sensory systems as a signaling component. We
found that 1 shows ratiometric and selective fluorescent
recognition of Zn2+ ions through the mechanism of internal
2
+
2+
6
Hg and Cd . It is still a challenge to develop a fluorescent
sensor with different metal-chelating ability and chelating
modes, which make its emission state modulated conveniently
9
charge transfer (ICT), and the recognition behavior can be
7
to create logic gates. From a literature search, the molecular
+
logic gates and/or switches on a single fluorescent sensor by K
Received: April 10, 2012
and Zn2 ions are still limited. In this regard, it is important
+
8
©
XXXX American Chemical Society
A
dx.doi.org/10.1021/ic300738e | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 1
+
modulated by K through the photoinduced electron-transfer
(
system was left undisturbed at room temperature. Brown block-shaped
11
crystals of 1-Zn were obtained after about 3 weeks. FT-IR (KBr pellets,
PET) mechanism. As a result, 1 can be used as a novel
−
1
cm ): 3447, 2925, 1622, 1559, 1490, 1447, 1363, 1340, 1264, 1223,
1135, 1054, 954, 779, 699. Anal. Calcd for C50 Cl : C,
0.40; H, 4.23; N, 11.75. Found: C, 50.64; H, 4.46; N, 11.39.
X-ray Data Collection and Structure Determinations. Single-
INHIBIT logic gate and an “off−on−off” molecular switch
triggered by Zn2 and K .
+
+
H50Zn
2
N
10
O
8
4
5
EXPERIMENTAL SECTION
Materials and General Methods. All of the starting materials for
synthesis were commercially available and were used as received. All of
the solvents used for titration measurements were purified by standard
procedures. H NMR spectra were measured in CDCl at 25 °C, and
H NMR titration was measured in CDCl /dimethyl sulfoxide
DMSO)-d with Varian Unity Plus 400 MHz NMR spectrometer
Varian, USA). Elemental analyses (C, H, and N) were performed on
a Perkin-Elmer 240C analyzer (Perkin-Elmer, USA). IR spectra were
measured on a TENSOR 27 OPUS FT-IR spectrometer with KBr
pellets in the range 4000−400 cm (Bruker, Germany). UV−vis
absorption spectra were measured with a Hitachi U-3010 UV−vis
spectrophotometer (Hitachi, Japan). Fluorescence spectra were
recorded at room temperature on a Varian Cary Eclipse fluorescence
spectrometer (Varian, USA).
crystal X-ray diffraction data for 1 was collected on a SCX-Mini
diffractometer at 293 K, and those for complex 1-Zn were collected on
a Rigaku RAXIS-RAPID diffractometer at 273 K with Mo Kα radiation
■
14
(
λ = 0.71073 Å) by ω scan mode. The program SAINT was used for
1
integration of the diffraction profiles. All of the structures were solved
by direct methods using the SHELXS program of the SHELXTL
package and refined by full-matrix least-squares methods with
SHELXL (semiempirical absorption corrections were applied using
3
1
3
(
6
(
1
5
the SADABS program). Metal atoms in complex 1-Zn were located
from E maps, and other non-H atoms were located in successive
difference Fourier syntheses and refined with anisotropic thermal
−1
2
parameters on F . The H atoms of the ligands were generated
theoretically onto the specific atoms and refined isotropically with
fixed thermal factors. Detailed crystallographic data are summarized in
2
+
Table S1 and the selected bond lengths and angles of 1 and 1-Zn are
given in Tables S2 and S3 in the Supporting Information.
Preparation of Solutions for Fluorometric and UV−Vis
+
+
2+
+
2+
2+
3+
2+
Theoretical Calculations. Theoretical investigations on 1 and 1-
Titration. Cations (K , Na , Ca , NH , Mg , Mn , Fe , Ni ,
4
16
2+
2+
+
+
2+
2+
2+
3+
2+
Zn were performed by the Gaussian03 program package method.
The geometrical structures of 1 and 1-Zn were fully optimized. The
optimized structure of the 1-Zn complex was very close to its single-
crystal X-ray diffraction structure.
Co , Cu , Cu , Ag , Hg , Cd , Zn , Eu , and Sr ) of 0.01 M in
acetonitrile were prepared. The concentration of 1 in fluorescence
titration tests was 50 μM with CH CN as the solvent. The UV−vis
titration concentration of 1 was studied in a CH CN solution with 5
3
3
μM. During titration, metal ions were added using the microinjector to
a solution of 1 (2.5 mL), and the whole volume of 1 and metal ions
could be considered as 2.5 mL because the volume of metal ions could
be ignored compared to that of 1. After stirring, the fluorescence
spectra were recorded. For all measurements, excitation and emission
slit widths were 5 nm.
RESULTS AND DISCUSSION
■
Absorbance and Fluorescence. The binding properties
+
+
2+
2+
2+
of 1 with different kinds of cations (K , Na , Ca , Mg , Sr ,
3
+
2+
+
2+
3+
2+
2+
2+
3+
+
Eu , Cu , Cu , Ni , Fe , Co , Hg , Mn , Nd , NH ,
4
2
+
+
2+
Synthesis of Fluorophore 1. As shown in Scheme 1, the
Cd , Ag , and Zn ) were investigated by UV−vis absorption
and fluorescence emission spectra. With an excitation wave-
length at 320 nm, 1 (50 μM) showed a strong emission peak at
13
intermediate compound 3 (210 mg, 0.5 mmol), 1,2-bis(pyridin-2-
yl)ethane-1,2-dione (212 mg, 1 mmol), and a few drops of acetic acid
as catalysts were dissolved in ethanol (20 mL) under a nitrogen
atmosphere, and the mixture was heated under reflux for ca. 4 h. The
reaction mixture was cooled and filtered to afford the crude product,
which was purified by recrystallization from C H OH to give 126 mg
2+
+
2+
3+
2+
2+
3
96 nm, and the addition of Cu , Cu , Ni , Fe , Co , Hg ,
2+
+
Mn , and Ag ions induced the fluorescence quenching of 1,
whereas very weak variations were observed upon the addition
2
5
+
+
2+
2+
2+
3+
3+
+
+
(
30%) of 1 as slight-yellow solid. ESI-MS: m/z 773.2 ([M + H] ).
of an excess of K , Na , Ca , Mg , Sr , Eu , Nd , and NH
cations, which show strong binding affinity with [2,4]dibenzo-
4
Anal. Calcd for C H N O : C, 68.38; H, 4.70; N, 14.50. Found: C,
6
4
4
4
36
8
6
1
17
2+
8.23; H, 4.59; N, 14.42. H NMR (CDCl -d , 400 MHz): δ 8.56 (m,
H), 7.76 (m, 8H), 7.45 (s, 4 H), 7.39 (s, 4H, quinoxaline phenyl
18-crown-6. Only the addition of Zn to the solution of 1
resulted in a prominent red shift of the fluorescence maximum
of about 64 nm from 396 to 460 nm (see Figure S2 in the
Supporting Information). Meanwhile, the ratio of the emission
3
6
proton), 4.37 (dd, J = 3.5 and 1.6 Hz, 8H), 4.13 (d, J = 2.2 Hz, 8H). IR
−1
(
KBr pellet, cm ): ν 1693, 1653, 1559, 1541, 1457, 1389. This
max
compound was further characterized by X-ray diffraction analysis (see
Figure S1 in the Supporting Information).
intensities at 396 and 460 nm (I4 /I396) changed from 0.09 to
60
2+
2
93.84 upon the addition of Zn . The fluorescence quantum
18
Synthesis of 1-Zn. In a tube, a mixture of 1:1 (v/v) CH Cl /
2
2
2
+
yield of 1 is 0.36 but increased to 0.75 upon Zn addition.
The results indicated that 1 can serve as a ratiometric
CH CN (10 mL) was carefully layered over a CH Cl (3 mL) solution
3
2
2
of 1 (0.05 mmol) as a buffer layer, over which a solution of ZnCl2
0.15 mmol) in CH CN (3 mL) was carefully added, and the resultant
2+
(
fluorescent sensor for Zn .
3
B
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Inorganic Chemistry
Article
The selectivity of the fluorescent response of 1 (50 μM) to
intensity can be completely covered by the broad one with high
intensity), which makes it difficult to accurately determine the
ratio of the two fluorescence peaks. As a result, it is usually
impossible to quantitatively analyze the target ions. However,
zinc ions was then examined in a CH CN solution (see Figure
3
+
1
). After Zn2 ions were added to the solution of 1, the
2
+
the two emission bands of 1 before and after binding Zn have
a low degree of overlap, and thus the ratio of the two
fluorescence peaks at 396 and 460 nm, respectively, can be well
determined. These data establish that 1 functions as a single-
2
+
excitation, dual-emission ratiometric probe for Zn .
When the cation metal interactes with the acceptor group,
the excited state is more stabilized by the cation than is the
ground state, and this leads to a red shift of the absorption and
4e,9a,12
emission spectra.
This mechanism is quite general, and
the experimental observations have been confirmed by the
density functional theory (DFT) calculation results, which will
be discussed later in this paper.
In addition, further investigation was carried out on the
2
+
changes of UV−vis spectra upon the addition of Zn ions to
the CH CN solution of 1 (5 μM; see Figure 2). With increasing
3
Figure 2. Absorption spectra of 1 (5 μM) in the presence of different
concentrations of Zn2 (0−8 equiv) in CH CN.
+
3
concentration of Zn2+ ions (0−8 equiv), the absorption peak at
365 nm was gradually decreased and a new peak at 396 nm
appeared simultaneously (red shift), accompanying the
appearance of two well-defined isosbestic points at 426 and
375 nm, indicating new species formed between 1 and Zn
ions. The interactions between 1 and zinc ions were also
Figure 1. (a) Fluorescence spectra (λ = 320 nm) of 1 (50 μM) in the
ex
2+
presence of different concentrations of Zn (0−2 equiv) in CH CN
3
(
2.5 mL). Both the excitation and emission slit widths were 5 nm.
Inset: Ratiometric combinational curve I (red) and I396 (black) as a
4
60
2+
2+
function of [Zn ] increased. (b) Visible emission observed from
samples of 1, 1-Zn , and 1 with other metal ions under a hand-held
UV−vis (365 nm) lamp: (A) only 1; (B) 1-Zn ; (C) 1 with other
2+
1
2+
studied by H NMR spectroscopy in a DMSO-d /CDCl
6
3
solution. Upon the addition of Zn2+ ions to the solution of 1,
the chemical shift of the pyridyl protons of 1 at 8.56 ppm
moves to 8.49 ppm, suggesting that coordination of Zn to the
metal ions.
2
+
6a
fluorescence intensity at 396 nm was gradually decreased,
pyridyl N atom occurred (see Figure S3 in the Supporting
2+
whereas the intensiy at 460 nm gradually increased and reached
Information). The coordination mode of Zn to 1 has been
characterized by single-crystal X-ray diffraction, which will be
described later in this paper.
2
+
a plateau after 2 equiv of Zn was added; meanwhile, a new
isoemissive point at 428 nm appeared, implying the formation
2
+
of a well-defined complex between Zn and 1. The solution of
A nonlinear fitting procedure of fluorescence titrations
2
+
2+
1
with 2 equiv of Zn ions converted the visual emission color
revealed that 1 coordinates with Zn in a 1:2 stoichiometry,
from dark to blue when excited with a hand-held 365 nm UV
lamp (Figure 1b). The red shift in the emission of 1 after Zn2+
coordination can be explained in terms of the ICT
and the binding constant is log β = 9.83 ± 0.04 (see Figure S4a
2
19
in the Supporting Information). The Job’s plot also suggests
that 1 formed the 1:2 complex with Zn2+ (see Figure S4b in the
Supporting Information). Furthermore, the electrospray
ionization mass spectrometry (ESI-MS) spectrum of the
complex cation displays peaks at m/z 900.4 (calcd m/z
3i,12
mechanism.
In general, a significant number of ICT-based
ratiometric fluorescence probes show broad fluorescence
spectra before and after binding target ions and have a high
degree of overlap (in some cases, the spectra with lower
2+
900.4) for [1-2Zn ] in acetonitrile, which also confirms the
C
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Inorganic Chemistry
Article
formation of 1-Zn2+ (see Figure S5 in the Supporting
Information).
ions, the emission band at 460 nm due to the 1-Zn2+ complex,
i.e., “on-state”, stood still unaffected (see Figure 3a). Reversely,
+
2+
Selection and Competition Experiments. A series of
interference experiments demonstrated that the presence of
other tested metal cations could hardly disturb 1 in recognizing
upon the addition of K ions to the mixture of 1 and Zn ions,
the emission band at 396 nm appeared again accompanied with
the disappearence of the emission band at 460 nm (see Figures
3b and S7 in the Supporting Information). Also, the
the Zn2 ion except for the K ion (see Figures 3a and S6a in
+
+
2+
fluorescence quantum yield of a 1-Zn solution was decreased
18
+
from 0.75 to 0.19 when K was added to it. It is interesting to
note that the fluorescence intensity of 1 was also affected by the
2
+
+
addition sequence of Zn and K . The fluorescent quenching
of 1 due to the addition of Zn2+ (0.2 mM) and then K (0.8
+
+
mM) was much greater than that due to the addition of K (0.8
mM) and then Zn2+ (0.2 mM; see Figures 3b and S7 in the
Supporting Information). Thus, we can conclude that the
different sequences of the addition of Zn2+ and K ions to the
+
solution of 1 in CH CN induced different emission changes,
3
permitting this complex could effectively act as an INHIBIT
molecular device of logic gate and on−off switch.
+
2+
Then, upon the addition of K ions to the solution of 1-Zn ,
the changes of the UV−vis spectra were similar to its emission
spectra, which could revive the original absorption spectra of 1
(
see Figure S8 in the Supporting Information). The addition of
2+
+
Zn ions to the solution of 1-K led to a decrease in the
intensity at 365 nm (see Figure S9 in the Supporting
2+
+
Information), while the addition of Zn /K ions to the
solution of 1 with different sequences could induce different
absorption spectral changes, indicating that 1 can obviously act
as a logic device as well. The fluorescence properties of 1 were
also studied in a 9:1 CH CN/H O solution, and the results
3
2
showed changes of fluorescence very similar to those in an
acetonitrile solution (see Figures S10 and S11 in the
Supporting Information).
Theoretical Studies. The time-dependent DFT by the
16
Gaussian 03 program was applied to make clear the changes
in the electronic properties. As we know, the highest occupied
molecular orbital (HOMO)−lowest unoccupied molecular
orbital (LUMO) gap and the electronic distributions may be
used to clarify the changes in the fluorescent properties with
metal cation coordination and detect the ratiometric response
20
to metal cations. In the case of free 1 (see Figure 4a), π
electrons on the HOMO mainly focus on the pyridyl units,
Figure 3. (a) Analysis of the maximum fluorescence intensity ratio at
+
4
3
60 nm of 1 (50 μM)) and 1-Zn2 with different cations (2 mM), λ =
ex
20 nm, λ = 460 nm; black, competing ions; red, competing ions +
Zn . (A) only 1, (B) Mg , (C) Na , (D) Ca , (E) Co , (F) Cu ,
G) Cu , (H) Eu , (I) Fe , (J) Hg , (K) Mn , (L) Nd , (M)
NH , (N) Ni , (O) Sr , (P) K , (Q) Cd , and (R) Ag . (b)
Fluorescence of 1 in a CH CN solution upon the addition of Zn and
K . (black) Only 1; (red) 1 with K (first 0.8 mM) and Zn (0.2
mM); (blue) 1 with Zn (0.2 mM); (cyan) 1 with Zn (0.2 mM,
em
2+
2+
+
2+
2+
+
2+
3+
3+
2+
2+
3+
(
+
2+
2+
+
2+
+
4
2+
3
+
+
2+
2+
2+
+
first) and K (0.8 mM).
+
the Supporting Information). So, the sequence of adding K
and Zn2 ions to the solution of 1 was investigated first to
+
explore whether it can lead to different fluorescence spectra. As
2
+
Figure 4. HOMO−LUMO energy gaps for respective compounds and
shown in Figure 3b, upon the addition of Zn (0.2 mM) to the
2+
interfacial plots of the orbitals: (a) free 1; (b) 1-Zn complex; (c) 1-
+
mixture of 1 and K ion, i.e., “off-state”, the emission band at
+
+
2+
K complex; (d) 1-K /Zn complex. Gray, red, and blue atoms of the
molecular frameworks indicate the C, O, N, and metal atoms,
respectively. Gray and deep-cyan parts on the interfacial plots refer to
the different phases of the molecular wave functions, for which the
isovalue is 0.02 au.
460 nm did not appear and the fluorescence spectra were
similar to that of free 1 (see Figures 3b and S6b in the
Supporting Information). However, upon the addition of Zn2+
to the mixture of 1 and the above-mentioned other tested metal
D
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Inorganic Chemistry
Article
Chart 1
Figure 5. View of the coordination geometry of Zn2+ in 1-Zn.
whereas those on the LUMO mainly focus on quinoxaline. In
(see Figure S6 in the SI). As illustrated in Figure 4d, the π
2
+
2+
+
2+
the presence of Zn ions, upon Zn binding with the N atom
of the pyridyl units, the energy levels of both HOMO and
LUMO are lower than those of free 1. The π electrons that
electrons on the HOMO of the 1-K /Zn complex are only
distributed on the chloride anions of zinc chloride, but the π
electrons on the LUMO are distributed on the quinoxaline. The
2
+
+
2+
focus on the LUMO of the 1:2 complex (1-Zn ) are
distributed on the pyridyl moiety, which makes the 1-Zn2+
complex stabilize the π electrons on the pyridyl moieties. Also,
the decreasing energy in the LUMO level is more significant
than that of the HOMO, indicating that the LUMO is more
stabilized. This results strongly proved the ICT from the
quinoxaline to the pyridyl moieties, which leads to a red shift in
the fluorescence spectra by stabilizing the energy levels of
LUMO upon interacting pyridine units with zinc ions (see
energies of both the HOMO and LUMO of the 1-K /Zn
+
complex are lower than those of the free 1 and 1-K complex.
+
2+
More importantly, the energy of the 1-K /Zn complex is
2
+
+
lower than that of the 1-Zn complex, indicating that the 1-K /
2+
Zn complex strongly promotes the PET process through
stabilization of the LUMO by the coordination of K and Zn
+
2+
with the crown and pyridyl moieties, respectively (Chart 1).
2
+
Crystal Structures. We can see that 1 and Zn form a
structure with 1:2 stoichiometry (see Figure 5). Single-crystal
X-ray determination reveals that compound 1-Zn crystallizes in
2
1
Figure 4b).
+
In the presence of K ions, the distribution of the π electrons
on HOMO and LUMO is similar to the free 1, which is mainly
located at pyridyl moieties and quinoxaline, respectively (see
̅
the triclinic space group P1. Both zinc centers adopt distorted
tetrahedral geometry through bidentate coordination of 1. Each
Zn ion is coordinated by two N atoms of pyridyl and two Cl−
2+
+
2+
Figure 4c). However, when both K and Zn ions are present,
ions, with the Zn−N bond lengths ranging from 2.045 to 2.071
́
the distribution of the π electrons on HOMO and LUMO is
Å. As shown in Figure 1, the dihedral angle between plane A
2
+
obviously unlike that of the 1-Zn complex (see Figure 4d).
(formed by N7, N8, O3, O4, etc.) and plane B (formed by N5,
N6, O1, O6, etc.) is 54.10°.
+
So, the presence of K ions blocked the ICT processes between
+
4e,22
1
and Zn2 ions
and caused the PET processes. Thus, the
Logic Gates and an Off−On−Off Switch Based on 1
2+
+
2+
+
addition of Zn ions to the mixture of 1-K only decreased the
fluorescence intensity of the band at 396 nm without a red shift
with Zn and K as the Inputs. It has been reported that
fluorescence sensors can act as logic gates, but the inputs of the
E
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Inorganic Chemistry
logic gates are mainly toxic heavy metals like Cu , Hg , and so
Article
2
+
2+
ASSOCIATED CONTENT
Supporting Information
■
6
,22
2+
on. As shown in Figure 6, when only Zn was added to the
*
S
Experimental procedures, characterization data for the syn-
thesis, crystal data, and calculated information, and X-ray
structural data for CCDC 849766 and 849767 in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
E-mail: buxh@nankai.edu.cn. Tel: +86-22-23502809. Fax:
86-22-23502458.
*
+
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
2
This work was supported by the 973 Program (Grant
012CB821700), NSFC (Grants 21031002 and 51073079),
and the NSF of Tianjin, China (Grant 10JCZDJC22100).
REFERENCES
■
Figure 6. Truth table (top) and the combinatorial logic scheme
(
1) For example, see: (a) Chimienti, F.; Devergnas, S.; Pattou, F.;
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(
bottom) of INHIBIT logic operations.
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6
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nm from 396 to 460 nm. However, upon the addition of both
K and Zn with different sequences, the fluorescence spectra
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+
2+
2
+
of 1 were changed differently. Furthermore, the effect of Zn
+
and K on the fluorescence of 1 can be used in a more
advanced molecular device, such as logic gates. A two-input
INHIBIT logic gate was successfully mimicked for 1. As shown
in Figure 6, K (input 1, 0.8 mM) and Zn (input 2, 0.2 mM)
were used as inputs; the emission band at 460 nm was taken as
the output in this system. The emission intensity at 460 nm was
distinctly high only when the inputs were in a (0, 1) sequence,
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(
3
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input INHIBIT logic gate was fabricated by using Zn2+ and K
while the output was low when inputs were (1, 0). Thus, a two+-
(
+
as inputs and taking I460 as the output. Moreover, when K was
2004, 8, 182. (i) Lim, N. C.; Freake, H. C.; Bruckner, C. Chem.Eur.
̈
2
+
added to the mixture of a 1-Zn solution, the emission bond at
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4
states (see Figure S7 in the Supporting Information);
meanwhile, the visible emission color of the 1-Zn2 complex+
solution was gradually disappearing upon the addition of K
+
(
see Figure S12 in the Supporting Information). As a result,
(
n) Tufan, B.; Akkaya, E. U. Org. Lett. 2002, 4, 2857.
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(
1
CONCLUSION
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■
A new chemosensor, 1, in which the 2,3-bis(pyridin-2-
yl)quinoxaline group was incorporated with a [2,4]dibenzo-
8-crown-6 core to form a ditopic environment and create two
1
different coordination modes for binding different kinds of
metal ions, has been well designed. We demonstrated that the
emission states and electronic distribution of 1 could be
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molecular device of a novel INHIBIT logic gate and an off−
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