A novel pyridine-containing half-salamo-based “on-off-on” fluorescent sensor for continuous detecting Cu2+ and S2?, and its structural features of copper(II) complex

Article abstract of DOI:10.1016/j.ica.2021.120344

A novel sensor PNS for the continuous recognition of Cu²⁺ and S^2? was synthesized, specifically recognizes Cu²⁺ in DMSO/H₂O (9:1 v/v) solution by fluorescence emission spectroscopy. The colour of the PNS solution changed from colourless to yellow when Cu²⁺ was added under the fluorescent lamp, and at excitation wavelengths of 301 and 365 nm, the violet fluorescence of the PNS solution was quenched. The PNS-Cu complex formed by the sensor PNS and Cu²⁺ can further identify S^2? in the fluorescence spectra. The LOD values of the two substances both Cu²⁺ and S^2? are 1.21 × 10^?8 and 5.58 × 10^?9 M. In addition, single crystals of the PNS-Cu complex were also obtained to verify the principle of this continuous identification process.

Full text of DOI:10.1016/j.ica.2021.120344

Inorganica Chimica Acta 521 (2021) 120344
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
A novel pyridine-containing half-salamo-based “on-off-on” fluorescent
sensor for continuous detecting Cu2 and S , and its structural features of
+
2ꢀ
copper(II) complex
*
Wen-Ze Zhang, Ruo-Yu Li, Peng Li, Zhuang-Zhuang Chen, Wen-Kui Dong
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, PR China
A R T I C L E I N F O
A B S T R A C T
A novel sensor PNS for the continuous recognition of Cu2 and S was synthesized, specifically recognizes Cu
+
2ꢀ
2+
Keywords:
Half-salamo-based probe
Copper(II) complex
Crystal structure
in DMSO/H O (9:1 v/v) solution by fluorescence emission spectroscopy. The colour of the PNS solution changed
2
2+
from colourless to yellow when Cu was added under the fluorescent lamp, and at excitation wavelengths of 301
and 365 nm, the violet fluorescence of the PNS solution was quenched. The PNS-Cu complex formed by the
Fluorescence recognition
Continuous identification
2
+
2ꢀ
sensor PNS and Cu can further identify S in the fluorescence spectra. The LOD values of the two substances
both Cu2 and S are 1.21 × 10 and 5.58 × 10 M. In addition, single crystals of the PNS-Cu complex were
+
2ꢀ
ꢀ 8
ꢀ 9
also obtained to verify the principle of this continuous identification process.
1
. Introduction
Copper(II) ion is indispensible component human body [1], and is an
substituents are introduced into the benzene rings of salamo-based li-
gands these changes lead to larger structural changes and new properties
of their corresponding complexes [15]. Some salamo- and bis(salamo)-
based sensors for the recognition of different ions have been investi-
gated in the past few years [16], the use of fluorescence as probes of half-
salamo-based compounds is rarely reported. Half-salamo-based ligands
not only have the stabilities of the salamo- and bis(salamo)-based li-
gands, but also retain a phenolic oxygen atom, which results in the
essential trace element, it plays a critical role in the function of many
cellular enzymes [2]. However, when excessive amounts of copper are
consumed, it can cause acute copper toxicity, hepatoenteric degenera-
tion, and intrahepatic cholestasis in children [3]. The detection of anions
in the environment by efficient, simple, and inexpensive techniques has
also been an area of extensive research in recent years [4]. As the
simplest sulfide anion, sulfide ions are widely distributed in wastewater
samples and in natural water samples [5]. High concentrations of sulfide
ions, an important indicator of water contamination, and excessive
concentrations can cause apoptosis, Alzheimer’s disease, and cirrhosis of
the liver [4e,5c]. Therefore, it is of great significance to develop a che-
mosensor to identify these two substances [5g,6].
3
formation of a cavity of N O. In this paper, a newly-designed half-sal-
amo-based sensor was synthesized, and which can continuously recog-
nize copper(II) and sulfide ions. The PNS-Cu complex formed by sensor
PNS and copper(II) ions can further recognize sulfide ions in solution.
This half-salamo-based complex sensor is a new type of probe derived
from half-salamo-based oxime-type sensor, which not only retains the
stability of salamo-based sensor in aqueous solutions and increases the
hydrophilicity of molecule, but also broadens the molecular construc-
tion of salamo-based sensor, which is important for improving the sys-
tem for the detection of inorganic salt content in aqueous solutions.
Currently, salen-based ligands and their derivatives continue to play
an important role in modern coordination chemistry due to their sig-
nificant applications in the fields of luminescence properties [7], cata-
lytic activities [8], electrochemistry [9], host–guest recognition [10],
magnetic materials [11], supramolecular structures [12] and bio-
activities [13], and are therefore of great research value. The intro-
duction of oxygen atoms onto salen-based ligands leads to the
2. Experimental section
2.1. Materials and measurements
2 2
production of salamo-based ligands [14] having a N O coordination
environment and a more stable molecular structure. When new
The reagents and materials used in this paper were all purchased
*
Corresponding author.
E-mail address: dongwk@126.com (W.-K. Dong).
https://doi.org/10.1016/j.ica.2021.120344
Received 11 January 2021; Received in revised form 5 March 2021; Accepted 5 March 2021
Available online 13 March 2021
0
020-1693/© 2021 Published by Elsevier B.V.

W.-Z. Zhang et al.
Inorganica Chimica Acta 521 (2021) 120344
Scheme 1. Synthetic route to PNS.
commercially and can be used directly without further purification. The
melting points of the compounds were measured using SGW X-4A
Shanghai Jingke Slight Melting Point Instrument (Shanghai, China). The
1
H NMR spectra were measured by an AVANCE DRX-400 / 500 spec-
3
trometer using CDCl as solvent (Bruke, Germany). C, H and N analyses
were performed via a GmbH VarioEL V3.00 automatic elemental ana-
lyser (Berlin, Germany). Elemental analyses for metal(II) were con-
ducted using an IRIS ER/S⋅WP ꢀ 1 ICP atomic emission spectrometer
(
Berlin, Germany). The fluorescence spectra of the probe PNS and the
PNS-Cu complex were measured by an F-7000 FL 220–240 V spectro-
photometer (Tokyo, Japan). X-ray single crystal structure determination
was carried out on SuperNova, Dual (Cu at zero) AtlasS2 four-circle
diffractometer.
2
.2. The synthetic route to probe PNS
The synthetic route to sensor PNS is presented in Scheme 1. First,
1
,2-dibromoethane (3.35 mL, 25.3 mmol) was added to the DMF solu-
Fig. 1. Fluorescence Intensity of PNS in DMSO solution at different water
content conditions. (λex = 301 nm, λem = 400 nm).
tion containing N-hydroxyphthalimide (8.10 g, 50.5 mmol) and stirred
thoroughly to obtain A1. An excess of hydrazine hydrate was added to
the ethanol solution of A1 under nitrogen-protected conditions and
stirred for 24 h to obtain A2. Then, 2-hydroxy-1-naphthaldehyde (172
mg, 1 mmol) was added drop by drop to the ethanol solution containing
5
dissolved in DMSO:H
2
O = 9:1 at a concentration of 1 × 10ꢀ M.
◦
A2 (92.1 mg, 1 mmol) and reacted at 55 C for 6 h to obtain N1. Finally,
2
.5. Solution selection for sensor PNS
Salamo-based ligand contains two electronegative oxygen atoms on
2
-formylpyridine (107 mg, 1 mmol) was slowly added to the ethanol
solution (20.0 mL) of N1 (246 mg, 1 mmol). The mixed solution was
◦
reacted at 55 C for 4 h. After purified by column chromatography, the
the basis of Salen-based ligand, its stability is significantly improved,
and overcomes the shortcomings of the easy hydrolysis of Salen-based
ligand. Previous studies have shown that Salamo-based fluorescent
probes do not hydrolyze in aqueous systems [2]. The sensor molecule
PNS has good solubility in methanol, ethanol, dichloromethane, tri-
chloromethane, acetonitrile, DMF and DMSO, but it has the strongest
excitation luminescence in DMSO, so DMSO was chosen as the liquid
environment for the sensor molecule. From Fig. 1, it can be concluded
that the water content in the solution increases, the fluorescence in-
tensity of the sensor molecule in solution gradually decreases. The
sensor has stronger fluorescence when the water content was less than
crude product was purified (petroleum ether:ethyl acetate = 6:1) to
obtain a white crystalline solid of sensor PNS 226 mg. Yield: 67.4%. M.
◦
p.: 72–74 C. Anal. Calc. for C19
17 3 3
H N O : C, 68.05; H, 5.11; N, 12.38%.
found: C, 68.24; H, 5.03; N, 12.57%.
2
.3. The preparation of sensor PNS-Cu solution
3 2
Weighing the sensor PNS (10.7 mg, 0.10 mmol) and Cu(NO ) (18.7
mg, 0.10 mmol), and then dissolving them in 10 mL DMSO solution,
◦
stirred at 50 C for 20 min. After cooling to room temperature, the so-
lution was diluted to 1 × 10ꢀ M and set aside.
5
4
0%, and the fluorescence tends to be constant when the water content
reached 50%. Therefore, a 9:1 solution of DMSO:H
test the sensor performance.
2
O was selected to
2
.4. Stock solution preparation for spectral detection
+
The cations of all anionic tested salts are Na and the anions of all
3. Results and discussion
ꢀ
metal salts used in all experiments are NO
3
. Stock solutions of the 16
2
+
3+
+
2+
+
2+
2+
2+
2+
2+
metal nitrates (Cd , Cr , Ag , Pb , Na , Co , Cu , Ni , Zn
,
3.1. The response of Cu to sensor PNS
2
+
3+
3+
+
2+
+
2+
Mg , Fe , Al , Li , Ca , K , and Mn ) and the 16 sodium salts
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
2+
(
H
2
PO
4
, NO
3
, I , HS , Br , F , SCN , Cl , AcO , NO
2
, HCO
3
, HPO
4
,
3.1.1. Fluorescence recognition of Cu
ꢀ
ꢀ
ꢀ
2+
ClO
4
, N
3
, CN and S ) were prepared in double distilled water at a
The fluorescence spectra of the sensor PNS to Cu were measured in
an DMSO:H O (9:1 v/v) solution, so the final concentration of the probe
ꢀ
4
concentration of 1 × 10
M. The sensors (PNS and PNS-Cu) are
2
2

W.-Z. Zhang et al.
Inorganica Chimica Acta 521 (2021) 120344
Fig. 5. Comparison of emission wavelengths at 400 nm for 16 cation fluores-
ꢀ
2+
5
+
3+
2+
Fig. 2. Fluorescence emission spectra of PNS (1 × 10 M) in the absence and
cence intensities at 301 nm excitation wavelength. (1 ~ 16 = Ag , Al , Ca
,
ꢀ 4
3+
+
2+
+
2+
2+
3+
3+
2+
+
2+
+
2+
2+
2+
+
2+
existence of different metal ions (1 × 10 M) (Cd , Cr , Ag , Pb , Na ,
Cd , Co , Cr , Fe , Zn , K , Mn , Na , Ni , Pb , Mg , Li and Cu ).
2
+
2+
2+
2+
2+
3+
3+
+
2+
+
2+
Co , Cu , Ni , Zn , Mg , Fe , Al , Li , Ca , K , and Mn ). (DMSO:
O = 9:1, λex = 301 nm, λem = 400 nm).
H
2
solution no longer changed significantly, thus it can be seen that sensor
2
+
PNS forms a stable PNS-Cu complex in the form of 1:1 with Cu ions in
2
solution. In addition, an extremely good linear correlation (R = 0.9013)
2
+
was obtained between the fluorescence intensity at 400 nm and the Cu
ion concentration in the range of 0 ~ 0.5 equivalents. The detection
limit of probe PNS for Cu2 was then calculated to be 1.21 × 10
+
ꢀ 8
M
based on the slope of the standard curve. These results indicate that
2
+
sensor PNS can be used to qualitatively monitor Cu . The complexes
formed by Cu2 ions and sensor PNS are very stable, and only S ions
+
2ꢀ
2
+
are known to displace Cu ions from sensor PNS, so the recognition of
2
+
Cu ions by sensor PNS can be considered as an irreversible process
without the involvement of S2 ions.
ꢀ
.1.2. Naked eye recognition of sensor PNS to Cu2
+
3
As can be seen in Fig. 4(a), after the addition of various metal ions to
sensor PNS, only the Cu2 ions can change the solution colour from
+
colourless to a distinctly bright yellow upon addition. Under the 365 nm
excitation light source, the Cu2 ions can also change the sensor PNS
solution colour significantly, which changes the solution colour from
purple to dark, as shown in Fig. 4(b). Thus, it can be determined that the
+
sensor PNS has specific recognition of Cu2 ions at excitation wave-
+
ꢀ
5
Fig. 3. Fluorescence emission spectra of sensor PNS (1 × 10 M) with adding
2
+
lengths of 301, 365 nm and sunlight.
Cu (0 ~ 1.0 equiv.). Inset: Naked eye identification of sensor PNS solution
2
+
before and after increase of Cu (1 equiv.).
+
3
.1.3. Selectivity of sensor PNS to Cu2
2
+
ꢀ 5
To evaluate the selectivity of sensor PNS for Cu ions, we have
was 1 × 10 M. As shown in Fig. 2, at an excitation wavelength of 301
nm, the sensor PNS possessed a fluorescence peak at about 400 nm.
When 10 equivalents of metal ions were added to 1 equivalents of PNS,
it was found that the characteristic peak of the sensor PNS at 400 nm
2
+
3+
+
2+
+
verified the competition of various cations (Cd , Cr , Ag , Pb , Na ,
2
+
2+
2+
2+
2+
3+
3+
+
2+
+
2+
Co , Cu , Ni , Zn , Mg , Fe , Al , Li , Ca , K , and Mn ) with
2
+
Cu ions in sensor PNS. The measurements were also repeated three
times to take the average value for analysis. From the cation competition
experiments in Fig. 5, it is evident that the sensor PNS has good iden-
tification properties for Cu2 ions and no interference from other cat-
disappear after the addition of Cu2 ions. The sensor PNS performs very
+
2
+
well in anti-interference experiment against Cu ions, and therefore has
the specificity to recognize Cu2 ions. The titration experiment of Cu
+
+
2+
ions, thus, sensor PNS has specific discrimination for Cu2 ions.
+
ions on sensor PNS in Fig. 3 showed that when an equivalent amount of
2
+
Cu ions was added to the solution, the fluorescence intensity of the
ꢀ
2+
5
ꢀ 5
Fig. 4. a) Colors of sensor PNS (1 × 10 M) upon addition of various metal ions. b) Fluorescence emission of sensor PNS (1 × 10 M) upon addition of various
2
+
3+
+
+
2+
2+
2+
2+
2+
3+
3+
+
2+
+
2+
metal ions. (no ion, Cd , Cr , Ag , Pb , Na , Co , Cu , Ni , Zn , Mg , Fe , Al , Li , Ca , K , and Mn ). (DMSO:H
2
O = 9:1, λex = 365 nm).
3

W.-Z. Zhang et al.
Inorganica Chimica Acta 521 (2021) 120344
Table 1
Crystal data and structure parameters for PNS-Cu.
The Cu(II) complex
PNS-Cu
4 6
16CuN O
Empirical formula
Formula weight
T (K)
C
19
H
242.86
100.00(11)
0.71073
Triclinic
P ꢀ 1
Wavelength (Å)
Crystal system
Space group
a (Å)
8.8614(4)
16.9853(8)
18.3238(9)
75.342(4)
89.162(4)
89.238(4)
2667.8(2)
12
b (Å)
c (Å)
◦
α
( )
◦
β ( )
◦
γ ( )
3
V (Å )
Z
ꢀ
3
D
calc (g∙cm
)
1.684
F (000)
1481
Crystal size (mm)
0.11 × 0.1 × 0.08
2.4490 to 26.9200
–11 ≤ h ≤ 12
◦
ꢀ 5
θ Range ( )
Index ranges
Fig. 7. Fluorescence emission spectra of PNS-Cu solution (1 × 10 M) in the
ꢀ 4
ꢀ
ꢀ
ꢀ
ꢀ
absence and existence of different anions (1 × 10 M) (H
2
PO
4
, NO
3
, I , HS ,
Index ranges Reflections collected/unique
–23 ≤ k ≤ 20
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
Br , F , SCN , Cl , AcO , NO
2
, HCO
3
, HPO
4
, ClO
4
, N
3
, CN and S ).
–
23 ≤ l ≤ 19
(
DMSO:H
2
O = 9:1, λex = 301 nm, λem = 475 nm).
1
2,451 / 7666 [Rint = 0.0591]
Completeness to θ
Data/restraints/parameters
GOF
99.42% (θ = 26.32)
12,451 / 0 / 811
1.017
about 475 nm after S2 (10 equivalents) was added.
ꢀ
2ꢀ
To evaluate the sensitivity of PNS-Cu to S , we investigated the
Final R , wR
2
, wR indices (all data)
1
2
indices
0.0635, 0.1040
0.1165, 0.1291
0.683 and ꢀ 0.792 e.Å
2ꢀ
titration experiment of PNS-Cu to S and recorded the changes of the
R
1
ꢀ
3
fluorescence spectra in this experiment. As shown in Fig. 8a, with
increasing S2 concentration, a brief fluorescence peak at about 400 nm
Largest diff. peak and hole
ꢀ
first appeared, followed by a gradual decrease, and the fluorescence
3
.1.4. Crystals structure
Single-crystal X-ray diffraction determination showed that the PNS-
Cu complex belongs to the triclinic crystal system with the space group P
1, which is described in Table 1. As shown in Fig. 6a and Table 1, the
ꢀ
PNS-Cu complex was found to be an asymmetric Cu(II) complex con-
ꢀ
sisting of one Cu(II) atom and one completely deprotonated ligand (L)
unit. In the structure of the PNS-Cu complex, the nitrate anion is
involved in the coordination. The five coordinated Cu(II) atom is located
ꢀ
in the N
3
O cavity of the fully deprotonated ligand (L) unit, using a
slightly distorted tetragonal cone geometry, as shown in Fig. 6b, which
shows the coordination polyhedron of the Cu(II) atom in the Cu(II)
complex. The attainment of this single crystal also verifies the correct-
ness of sensor PNS and sensor PNS-Cu recognition mechanism in this
paper.
3
3
.2. The response of S2 to sensor PNS-Cu
ꢀ
.2.1. Fluorescence recognition of S2
The fluorescence properties of the sensor PNS-Cu (1 × 10 M) were
tested at DMSO:H
ꢀ
ꢀ 5
ꢀ 5
Fig. 8. a) Fluorescence emission spectra of sensor PNS-Cu (1 × 10 M) with
2
O = 9:1. As shown in Fig. 7, the free sensor PNS-Cu
2
ꢀ
adding S (0 ~ 1.5 equiv.). Inset: Naked eye identification of sensor PNS so-
has no fluorescence emission peak at 400–600 nm, a relatively small
fluorescence peak appears at 400 nm when other anions (10 equiva-
lents) were added, and a strong cyan-blue fluorescence peak appears at
2
ꢀ
lution before and after increase of S (1.5 equiv.). b) Fluorescence intensity at
2
ꢀ
4
75 nm with S ion titration curve. (λex = 301 nm).
Fig. 6. a) Crystal structure of PNS-Cu. b) Coordination environment for Cu(II) atom.
4

W.-Z. Zhang et al.
Inorganica Chimica Acta 521 (2021) 120344
Fig. 9. Comparison of 16 anion fluorescence intensities at 475 nm emission
ꢀ
ꢀ
ꢀ
wavelength at 301 nm excitation wavelength. (1 ~ 16 = H
4 4 3 3 2 3
2
PO
4
, AcO , Br ,
Fig. 11. Fluorescence intensities measured at different pH values.
ꢀ
ꢀ ꢀ ꢀ 2ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ 2ꢀ
Cl , ClO , CN , F , HPO , HS , I , N , NO , NO , SCN , HCO , and S ).
.2.2. Selectivity of sensor PNS-Cu to S2
ꢀ
3
To evaluate the selectivity of sensor PNS-Cu for S2 ions, we have
ꢀ
intensity at 475 nm gradually increased (Fig. 8a) and stabilized after 1.5
eq. Moreover, an excellent linear relationship (R2 = 0.9672) was also
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
verified the competition of various anions (H PO , NO , I , HS , Br ,
2
4
3
obtained between the fluorescence intensity at 475 nm and the S2
ꢀ
ꢀ ꢀ ꢀ ꢀ ꢀ ꢀ 2ꢀ ꢀ ꢀ ꢀ 2ꢀ
F , SCN , Cl , AcO , NO , HCO , HPO , ClO , N , CN and S ) with
2 3 4 4 3
2
ꢀ
ions in sensor PNS-Cu. The measurements were also repeated three
concentration in the range of 0 ~ 1.5 equivalents (Fig. 8b). Finally, the
S
2
ꢀ
6
binding constant K for PNS-Cu and S was estimated to be 1.79 × 10
times to take the average value for analysis. In the competitive experi-
ꢀ 1
M
by the Scatchard equation, and the result indicates that the reaction
ment, it was found that the fluorescence enhancement was relatively
2
ꢀ
2ꢀ
of PNS-Cu and S has a particularly high stability. The detection limit
weak after the addition of a few anions to the solution containing S
,
of PNS-Cu for S2 was then calculated to be 5.58 × 10 M based on the
ꢀ
ꢀ 9
which might be caused by the change of the solution fluorescence due to
the decrease of the solution concentration after the addition of other
anions, but the fluorescence intensity of the solution was still signifi-
cantly enhanced.
slope of the standard curve. These results indicate that PNS-Cu can
qualitatively monitor S2 and then further optimized.
ꢀ
In this way, the maximum emission wavelength is red-shifted, which
2
ꢀ
indicates that no new bonds are formed between PNS-Cu and S during
the bonding process. It is speculated that the fluorescence change may
be due to a simple displacement reaction process and the formation of
stable compounds of CuS after ion exchange.
In the anion competition experiments of Fig. 9, other anions also did
2
ꢀ
not significantly interfere with S ions, so sensor PNS-Cu has specific
recognition of S2
ꢀ
.
ꢀ
ꢀ
Fig. 10. Density functional theory (DFT) calculations of sensor PNS, PNS-Cu, and fluorescent molecule PNS . Left: PNS; Medium: PNS-Cu; Right: PNS .
5

W.-Z. Zhang et al.
Inorganica Chimica Acta 521 (2021) 120344
Table 2
2
+
Comparison of different sensors for Cu detection.
System
Signal output
Colorimetry
Linear range (
μ
M)
LOD (M)
1.02 × 10ꢀ
References
[16a]
6
0–20
2.05 × 10ꢀ
7
[18]
Fluorescence
0–20
2.67 × 10ꢀ
8
[2b]
Fluorescence
0–5
3.27 × 10ꢀ
1.52 × 10ꢀ
8
8
[23]
[24]
Fluorescence
Fluorescence
0–10
0–15
4.47 × 10ꢀ
7
[25]
Fluorescence
0–10
8
Colorimetry
Colorimetry
0–5
2.81 × 10ꢀ
[26]
[27]
7
0–400
1.5 × 10ꢀ
2.26 × 10ꢀ
6
[28]
Colorimetry
0–20
1.21 × 10ꢀ
8
This work
PNS
Fluorescence
0–5
6

W.-Z. Zhang et al.
Inorganica Chimica Acta 521 (2021) 120344
Table 3
2
ꢀ
Comparison of different sensors for S detection.
System
Signal output
Linear range (μM)
LOD (M)
References
ꢀ
ꢀ
7
9
ABTS–Au (III) system
Colorimetry
Colorimetry
0.5–15
0–3.5
2.8 × 10
5.7 × 10
[19]
[20]
ꢀ
ꢀ 8
8
Bare Au nanoparticles colorimetry
Colorimetry
Fluorescence
Fluorescence
0.5–10
0.1–8.0
0–7.5
8 × 10
6 × 10
[21]
[22]
[6b]
2
+
CDs/PEI/NB/Cu
ꢀ
9
1.2 × 10
8
Fluorescence
Fluorescence
0–15
0–10
1.79 × 10ꢀ
[24]
[25]
9.12 × 10ꢀ
7
7
Colorimetry
Fluorescence
1.5–90
0–15
3.35 × 10ꢀ
[29]
9
PNS-Cu
5.58 × 10ꢀ
This work
ꢀ
3
.3. The sensing mechanism of sensor PNS-Cu to S2
Cu complex. More importantly, the HOMO-LUMO energy gap before
and after the interaction of sensor PNS with Cu2 also decreased from
+
2
+
In order to further understand the reaction mechanism of these two
4.041 eV to 2.418 eV. in other words, the combination of Cu and
sensor PNS made the system more stable. Thus, we speculate that the
fluorescence quenching mechanism of the interaction between sensor
sensors, we analyzed the ion state in the solution under different con-
ditions during continuous sensing by mass spectrometry. We know from
the mass spectrometry under different conditions that when sensor PNS
detects Cu2 ions in the solution, the free copper(II) ions in the solution
combine with sensor PNS to form a new complex, which quenched the
fluorescence of the PNS solution that originally emits fluorescence, as
shown in Figs. S2 and S3. During the detection of the anions by sensor
PNS-Cu, the free S2 ions in the solution combine with the copper(II)
ions in the sensor, and the original copper(II) ions in the sensor were
quenched by the fluorescence. The position of the ion is occupied by the
PNS and Cu2 ions is photo-induced electron transfer (PET), as shown in
+
+
2+
Fig. 10. Before the binding of sensor and Cu ions, when the sensor was
transferred from the fundamental state to the excited state via the
excited light source, no significant electron transfer occurred and there
was no significant change in fluorescence. However, after the combi-
ꢀ
2+
nation of PNS and Cu ions, the excited state electrons on the PNS-Cu
complex were transferred to the Cu2 ions, so that the excited state
electrons on the PNS-Cu complex could not return to the ground state,
and fluorescence quenching occurred. After the introduction of sodium
+
+
Na ion in the solution, and the solution resumes fluorescence, as shown
2
ꢀ
in Figure S3.
sulfide, the copper(II) element in the complex combined with S to
form a copper(II) sulfide precipitate, and the electron transfer process,
which was originally blocked, was reopened, so that fluorescence
appeared again. The calculated results are just in agreement with the
speculated mechanism.
3
.4. DFT-theoretical analysis of the sensing mechanism
The electron distributions of PNS and PNS-Cu before and after
sensing with the target ions by Gaussian 09 program density functional
theory (DFT) [17]. Density functional theory (DFT) calculations showed
that the HOMO-LUMO orbital electron clouds of sensor PNS are
distributed on the side of the naphthalene ring of the luminescent group
3.5. Effect of pH
In practical applications, the sensor also needs to be applied to
physiological pH, so we measured the fluorescence intensity at different
of the molecule, and after binding with Cu2 ion, the HOMO-LUMO
+
2
+
2+
2ꢀ
orbital electron clouds are shifted towards Cu and pyridine. When
pH values after adding Cu and S to PNS, respectively, as shown in
Fig. 11. It was found that the fluorescence intensity of the PNS solution
is weak in the pH range of 2 ~ 3, which can be attributed to negligible
deactivation in strongly acidic solutions, and is significantly enhanced
between 4 and 11. PNS can be said to be relatively stable in this range.
PNS-Cu solutions are also suitable between 3 and 11. The pH values
2
ꢀ
2+
the S ion snatches the Cu ion from the sensor PNS-Cu, the HOMO
orbital electron cloud of the molecule is shifted back to the luminescence
group, thus making the solution fluorescent again. In addition, the en-
ergy LUMO (ꢀ 2.067 eV) is lower than that of the fluorophore LUMO
(
ꢀ 1.512 eV) in the sensor PNS due to the calculated energy in the PNS-
7

W.-Z. Zhang et al.
Inorganica Chimica Acta 521 (2021) 120344
measured after the addition of S2 to the PNS-Cu solution showed slight
fluctuations between 4 and 11 and showed a strong fluorescence in-
tensity in this range. After pH = 12, it is not discussed further as the
solution’s alkaline test molecule’s luminescence is enhanced and not
ꢀ
[2] (a) J.Y. Uriu-Adams, C.L. Keen, Mol. Aspects. Med. 26 (2005) 268–298;
(
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2
+
(b) L. Tang, P. Zhou, Q. Zhang, Z. Huang, J. Zhao, M. Cai, Inorg. Chem. Commun.
easily detected. PNS was found to be stable for the detection of Cu and
3
6 (2013) 100–104;
2
ꢀ
S
in the pH range of 4 ~ 11. This solution can be used as an excellent
(
c) A. Mohammadi, J. Jabbari, J. Enviro. Chem. Eng. 94 (2016) 631–636;
chemical sensor.
(d) A. Mohammadi, M. Kianfar, J. Photochem. Photobio. A 367 (2018) 22–31;
(
(
e) F.S. Zabihi, A. Mohammadi, Spectrochim. Acta A 238 (2020), 118439;
f) M. Yu, H.R. Mu, L.Z. Liu, N. Li, Y. Bai, X.Y. Dong, Chin. J. Inorg. Chem. 35
3
.6. Comparison between PNS and other probes
From Table 2, it can be observed that among the four Cu2 fluores-
(2019) 1109–1120.
[
5] (a) N. Paul, R. Sarkar, R. Sarkar, A. Barui, S. Sarkar, J. Chem. Enc. 132 (2020) 21;
(b) A. Paul, S. Anbu, G. Sharma, M.L. Kuznetsov, M.F.C.G.D. Silva, B. Kochb, A.J.
L. Pombeiro, Dalton Trans. 44 (2015) 16953–16964;
+
cence probes, sensor PNS has a lower detection limit for recognizing
(c) O. Choi, T.E. Clevenger, B. Deng, R.Y. Surampalli, L. Ross Jr, Z. Hu, Water Res.
4
3 (2009) 1879–1886;
copper(II) ions than the relative sensors in other articles [2b,6b,18].
2
ꢀ
(d) D.Y. Park, K.Y. Ryu, J.A. Kim, S.Y. Kim, C. Kim, Tetrahedron 72 (2016)
3
(e) C.S. Kwan, T. Wang, S.M. Chan, Z.W. Cai, K.C.F. Leung, Dalton Trans. 538
Also, in Table 3, sensor PNS-Cu has improved sensitivity to S
930–3938;
compared to the other four S2 probes [19–22]. It is thus clear that
sensor PNS and PNS-Cu are more sensitive than the other relative sen-
sors in the above table.
ꢀ
(2020) 528–532;
(
f) X.J. Yan, Z.G. Wang, Y. Wang, Y.Y. Huang, H.B. Liu, C.Z. Xie, Q.Z. Li, J.Y. Xu,
Spectrochim. Acta A 243 (2020), 118797;
g) X.X. An, Z.Z. Chen, H.R. Mu, L. Zhao, Inorg. Chim. Acta 511 (2020), 119823.
(
[
[
6] (a) Y. Feng, Y. Yang, Y.Z. Wang, F.Z. Qiu, X.R. Song, X.L. Tang, G.L. Zhang, W.
4
. Conclusion
S. Liu, Sens. Actuators B 288 (2019) 27–37;
(
b) J.F. Wang, T. Feng, Y.J. Li, Y.X. Sun, W.K. Dong, Y.J. Ding, J. Mol. Struct. 1231
A novel half-salomo-based chemical sensor PNS was synthesized
(2021), 129950;
2
+
2ꢀ
firstly, and can continuously recognize Cu and S ions in solution.
(c) L. Xu, M. Yu, L.H. Li, J.C. Ma, W.K. Dong, J. Struct. Chem. 60 (2019)
1358–1365.
2
+
Sensor PNS has a high binding constant to Cu ions and a detection
7] (a) Z.L. Wei, L. Wang, J.F. Wang, W.T. Guo, Y. Zhang, W.K. Dong, Spectrochim.
Acta A 228 (2020), 117775;
ꢀ 8
2+
limit of 1.21 × 10 M, and can recognize Cu ions with the naked eye
under both 301 and 365 nm excitation light sources. The new sensor
(b) Y. Zhang, L.Z. Liu, Y.D. Peng, N. Li, W.K. Dong, Transit. Metal. Chem. 44
(2019) 627–639;
PNS-Cu combined by PNS with Cu2 ions can further recognize S ions
+
2ꢀ
(
c) R.N. Bian, J.F. Wang, Y.J. Li, Y. Zhang, W.K. Dong, J. Photochem. Photobio. A
ꢀ 9
in solution and has a lower detection limit of 5.58 × 10 M. It has also
been demonstrated that the half-salomo-based complex chemical sensor,
which are derived from the half-ssalomo-based sensor PNS, can also be
used to detect ions in aqueous solutions.
4
00 (2020), 112719;
(d) Z.L. Wei, L. Wang, S.Z. Guo, Y. Zhang, W.K. Dong, RSC Adv. 9 (2019)
1298–41304;
e) H.R. Mu, X.X. An, C. Liu, Y. Zhang, W.K. Dong, J. Struct. Chem. 61 (2020)
155–1166;
f) X. Xu, F. Tao, S.S. Feng, W.K. Dong, Appl. Organomet. Chem. 35 (2021), e6057.
8] (a) Q.P. Kang, X.Y. Li, Z.L. Wei, Y. Zhang, W.K. Dong, Polyhedron 165 (2019)
8–50;
b) X.Y. Li, Q.P. Kang, C. Liu, Y. Zhang, W.K. Dong, New J. Chem. 43 (2019)
4
(
1
(
[
CRediT authorship contribution statement
3
(
Wen-Ze Zhang: Data curation, Formal analysis, Investigation,
Methodology, Project administration, Writing - original draft. Ruo-Yu
Li: Data curation, Formal analysis, Investigation, Methodology. Peng Li:
Project administration, Software. Zhuang-Zhuang Chen: Formal anal-
ysis, Investigation. Wen-Kui Dong: Project administration, Conceptu-
alization, Funding acquisition, Resources, Supervision.
4605–4619;
(
(
(
c) X.X. An, Q. Zhao, H.R. Mu, W.K. Dong, Crystals 9 (2019) 101;
d) Q. Zhao, X.X. An, L.Z. Liu, W.K. Dong, Inorg. Chim. Acta 490 (2019) 6–15;
e) S.Z. Guo, Y.J. Lia, S.S. Feng, W.K. Dong, Russ. J. Gen. Chem. 90 (2020) 1–9.
[9] L.Q. Chai, L.J. Tang, L.C. Chen, J.J. Huang, Polyhedron 122 (2017) 228–240.
[
10] (a) X.X. An, C. Liu, Z.Z. Chen, K.F. Xie, W.K. Dong, Crystals 9 (2019) 602;
(
(
(
(
(
(
b) Y.F. Cui, Y. Zhang, K.F. Xie, W.K. Dong, Crystals 9 (2019) 596;
c) Y. Zhang, Y.Q. Pan, M. Yu, X. Xu, W.K. Dong, Appl. Organomet. Chem. 33
2019), e5240;
d) P. Li, G.X. Yao, M. Li, W.K. Dong, Polyhedron 195 (2021), 114981;
e) J.F. Wang, X. Xu, R.N. Bian, W.K. Dong, Y.J. Ding, Inorg. Chim. Acta 516
2021), 120095.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[11] (a) Y. Zhang, M. Yu, Y.Q. Pan, Y. Zhang, L. Xu, X.Y. Dong, Appl. Organomet.
Chem. 34 (2020), e5442;
(
(
b) L.W. Zhang, Y. Zhang, Y.F. Cui, M. Yu, W.K. Dong, Inorg. Chim. Acta 506
2020), 119534.
[
12] (a) Y.Q. Pan, Y. Zhang, M. Yu, Y. Zhang, L. Wang, Appl. Organomet. Chem. 34
(
(
(
(
1
(
2020), e5441;
Acknowledgments
b) L. Wang, Z.L. Wei, Y.Q. Pan, Y. Zhang, W.K. Dong, Chin. J. Inorg. Chem. 35
2019) 1791–1804;
c) L.Z. Liu, M. Yu, X.Y. Li, Q.P. Kang, W.K. Dong, Chin. J. Inorg. Chem. 35 (2019)
This work was supported by the National Natural Science findation
of China (21761018) and the Program for Excellent Team of Scientific
Research in Lanzhou Jiaotong University (201706), both of which are
gratefully acknowledged.
283–1294;
d) S.Z. Zhang, J. Chang, H.J. Zhang, Y.X. Sun, Y. Wu, Y.B. Wang, Chin. J. Inorg.
Chem. 36 (2020) 503–514;
(
(
e) J. Li, H.J. Zhang, J. Chang, Y.X. Sun, Y.Q. Huang, Crystals 8 (2018) 176;
f) H.J. Zhang, J. Chang, H.R. Jia, Y.X. Sun, Chin. J. Inorg. Chem. 34 (2018)
2
261–2270;
g) J. Chang, H.J. Zhang, H.R. Jia, Y.X. Sun, Chin. J. Inorg. Chem. 34 (2018)
097–2107;
h) H.R. Jia, J. Chang, H.J. Zhang, J. Li, Y.X. Sun, Crystals 8 (2018) 272.
[13] (a) L. Wang, Z.L. Wei, Z.Z. Chen, C. Liu, W.K. Dong, Y.J. Ding, Microchem. 155
(
2
(
Declaration of Competing Interest
There are no conflicts of interest to declare.
Appendix A. Supplementary data
(
(
(
2020), 119823;
b) R.N. Bian, J.F. Wang, X. Xu, X.Y. Dong, Y.J. Ding, Appl. Organomet. Chem. 35
2021), e6040.
[
14] (a) M. Yu, Y. Zhang, Y.Q. Pan, L. Wang, Inorg. Chim. Acta 509 (2020), 119701;
(
(
1
(
3
b) Y.X. Sun, Y.Q. Pan, X. Xu, Y. Zhang, Crystals 9 (2019) 607;
c) L. Wang, Z.L. Wei, Z.Z. Chen, C. Liu, W.K. Dong, Microchem. 155 (2020),
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.ica.2021.120344.
04801;
d) C. Liu, Z.L. Wei, H.R. Mu, W.K. Dong, Y.J. Ding, J. Photochem. Photobio. A
97 (2020), 112569;
e) R.N. Bian, J.F. Wang, Y.J. Li, Y. Zhang, W.K. Dong, J. Photochem. Photobiol. A
00 (2020), 112829;
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