A dual probe for selective sensing of Zn (II) by fluorescent and Cu (II) by colorimetric methods in different systems based on 7,8-benzochromone-3-carbaldehyde -(fluorescein)hydrazone

Article abstract of DOI:10.1016/j.jphotochem.2020.113007

In this study, a novel fluorescent probe sensor, 7,8-benzochromone-3-carbaldehyde (fluorescein)hydrazone L, was designed and synthesized. Based on the photoinduced electron transfer (PET) process, L can detect Zn²⁺ in the solution of EtOH/H₂O (9/1, V/V). The probe had high selectivity and sensitivity to Zn²⁺ with a lower detection limit of 3.4 × 10^?7 M. Furthermore, the coordination ratio of L-Zn²⁺ was 1:1, which could be corroborated by Job's plot. In addition, in the EtOH/ H₂O (5/2, V/V) solution of the probe L, Cu²⁺ was added to produce a marked change in color from achromatous to yellow, indicating that the probe L could detect Cu²⁺ by colorimetry, which was detectable by the naked eye, simply and quickly. According to the Benesi-Hildebrand equation, the complexing constants values of L-Zn²⁺ and L-Cu²⁺ were 9.8 × 10⁴ M^-1 and 1.009 × 10⁵ M^-1, respectively.

Full text of DOI:10.1016/j.jphotochem.2020.113007

Journal of Photochemistry & Photobiology, A: Chemistry 406 (2021) 113007
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology, A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
A dual probe for selective sensing of Zn (II) by fluorescent and Cu (II) by
colorimetric methods in different systems based on 7,8-benzochromo-
ne-3-carbaldehyde -(fluorescein)hydrazone
Jie Sun, Tian-rong Li*, Cong Liu, Jia Xue, Li-mei Tian, Kui Liu, Si-liang Li, Zheng-yin Yang*
College of Chemistry and Chemical Engineering, State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, a novel fluorescent probe sensor, 7,8-benzochromone-3-carbaldehyde (fluorescein)hydrazone L,
Fluorescent probe
Benzochromone hydrazone
2+
was designed and synthesized. Based on the photoinduced electron transfer (PET) process, L can detect Zn in
2+
the solution of EtOH/H
2
O (9/1, V/V). The probe had high selectivity and sensitivity to Zn with a lower
2
+
+
Zn
Cu
ꢀ 7
2+
detection limit of 3.4 × 10
M. Furthermore, the coordination ratio of L-Zn
was 1:1, which could be
2
corroborated by Job’s plot. In addition, in the EtOH/ H
2
O (5/2, V/V) solution of the probe L, Cu2 was added to
+
Colorimetry
2
+
produce a marked change in color from achromatous to yellow, indicating that the probe L could detect Cu by
colorimetry, which was detectable by the naked eye, simply and quickly. According to the Benesi-Hildebrand
equation, the complexing constants values of L-Zn2 and L-Cu were 9.8 × 10
+
2+
4
M
-1
and 1.009 × 10 M ,
5
-1
respectively.
1
. Introduction
in the body is a key factor in maintaining the health of the body. Due to
the widespread use of zinc in the smelting industry, it has caused serious
environmental pollution [26]. In a word, it is necessary to design and
synthesize a fluorescent chemical sensor to realize the detection of zinc
and copper.
It is widely known that zinc as a transition metal element ranks
second in the human body (second only to iron), and also an essential
2
+
trace element for animals and plants [1–3]. Zn plays a vital role in
biological activities due to its various coordination methods [4,5]. For
example, as one of the auxiliary enzyme components required by many
human metabolisms, it regulates the metabolism of the human body, the
transmission of neural signals, the transcription and translation of genes,
etc [6–10]. At the same time, zinc is a common mineral in the human
body. If the content of zinc is insufficient, it would affect children’s in-
tellectual development. On the other hand, when the accumulation of
The method of fluorescence detection has the advantages of high
selectivity, high sensitivity and low detection limit compared with the
previous traditional detection methods, such as atomic absorption
spectroscopy and atomic emission spectroscopy [27–31]. In view of the
above advantages, the method of fluorescence detection is widely
applied in ion detection. The fluorescent probe reported in this article
has high selectivity and high sensitivity for the detection of metal ions
and it is designed and synthesized based on the fluorescence detection
method. Herein, the sensor we designed is synthesized by using Schiff
2
+
Zn reaches high levels in human body, it can increase the risk of
cardiovascular and cerebrovascular diseases [11–16]. In the same way,
as the third most abundant transition metal element in the human body,
copper is also an indispensable important participant in many life pro-
cesses [17]. Copper plays a vital role in nerve transmission, oxygen
transport, redox, etc [6,18]. However, excessive concentration in cells or
tissues of organisms can cause neurodegenerative diseases such as Alz-
base as
a raw material. The Schiff base structure provides an
electron-rich environment, making it easy to combine with metal ions.
Therefore, Schiff base can be regarded as a good ligand [32–34]. In
recent years, an increasing number of fluorescent sensors have been
exploited to detect metal ions. For instance, Gao et al. compounded a
2
+
2+
heimer’s disease, Monks’ disease, Wilson’s disease, etc [19–23]. Cu
can also be used to be a cofactor for metalloenzymes and proteins in
organisms [24,25]. Hence, maintaining proper levels of copper and zinc
N-(benzimidazol-2-yl) salicylaldimine (H
2
L) to detect Zn in dimethyl
sulfoxide [1]. Fu et al. synthesized QS to detect Zn2 in EtOH/H
+
2
O (4/1,
V/V) [2]. In this article, we report the synthesis of the probe 7,
*
Corresponding authors.
E-mail addresses: litr@lzu.edu.cn (T.-r. Li), yangzy@lzu.edu.cn (Z.-y. Yang).
https://doi.org/10.1016/j.jphotochem.2020.113007
Received 14 September 2020; Received in revised form 24 October 2020; Accepted 27 October 2020
Available online 4 November 2020
1
010-6030/© 2020 Elsevier B.V. All rights reserved.

J. Sun et al.
Journal of Photochemistry & Photobiology, A: Chemistry 406 (2021) 113007
8
-benzochromone-3-carbaldehyde-(fluorescein)hydrazone with the
2.3. Measurement of UV–vis and fluorescence spectra
2
+
2+
fluorescence test of Zn and the colorimetric test of Cu in different
solvents with this probe. It is necessary to mention that the colorimetric
detection of Cu2 can be observed with the naked eye which is simple
ꢀ 3
+
+
+
2+
Stock solutions (5 × 10 M) of various metal ions (Na , K , Li ,
+
+
2+
3+
2+
3+
ꢀ
2+
3+
2+
2+
2+
2+
2+
2+
Ag , Ca , Ba , Mg , Zn , Cu , Hg , Pb , Mn , Ni , Co ,
2
+
and quick to detect ions [35,36].
Cd , Fe , Cr , Al ) were prepared in ethanol. Stock solution of
3
probe L (5 × 10 M) was obtain in DMF.
In the fluorescence spectroscopy tests, the mixed solution of L (20 L)
μ
2
. Experimental
and various metal ions (20
μ
L) was added to the cuvette and diluted with
EtOH/H O solution (9/1, V/V) to 2 mL. For the setting of parameters,
2
2
.1. Materials and instruments
the excitation wavelength was set to 428 nm, and the excitation and the
emission slit were set to 5 nm and 3 nm, respectively. The detection
method of UV–vis spectroscopy was basically the same as that of fluo-
rescence. The only difference was that the diluent of the mixed solution
All reagents in this experimentation were sourced from commodity
suppliers and no further purification was performed when used. Ultra-
pure water was used in this experiment. Fluorescence spectrum, UV
absorption spectrum, ESI-MS spectrum and 1H NMR spectrum were
of L (10
μ
μ
2
L) and various metal ions (10 L) was EtOH/H O solution (5/2,
ꢀ 1
V/V).
obtained by Hitachi RF-4500 spectrometer equipped with 1 cm quartz
cuvette, Shimzdzu UV-240 spectrophotometer, Bruker Esquire 600
spectrometer and Bruker 400 MHz with TMS as the internal standard,
respectively. The melting point was measured on a Beijing XT4-100x
micro-melting point instrument.
3
. Results and discussion
.1. Effect of solvent
The solvent had a crucial influence on the coordination of the probe L
3
2
.2. Synthesis
-oxo-4H-benzo[h]methylene-3-carbaldehyde [37] and fluorescein
with the metal ion. In order to explore the most suitable solvent for
detecting the coordination of L and Zn2 , the solvent selection experi-
ment was carried out by the fluorescence spectrum. When the ability of L
to recognize various metal ions was studied in ethanol solution, we
+
4
hydrazide [38] were synthesized according to methods reported in
previous literature. Based on the following method, 7,8-benzochromo-
ne-3-carbaldehyde-(fluorescein)hydrazone (Scheme 1) was synthe-
sized, fluorescein hydrazide (0.24 g, 0.7 mmol) and 4-oxo-4H-benzo[h]
methylene-3-carbaldehyde (0.16 g, 0.7 mmol) was dissolved in an
appropriate amount of ethanol. The mixture was refluxed for 24 h under
stirred condition with appearance of pale yellow precipitate. After that,
the mixture was cooled to room temperature and filtered under reduced
pressure to obtain a crude product. The obtained crude product was
recrystallized from ethanol and then the product was dried in a vacuum
2+
found that L showed obvious fluorescence upon addition of Zn or
2+
2+
2+
Mg . Therefore, we tried to distinguish between Zn and Mg by
2+
2+
changing the solvent. Zn or Mg was added into ethanol, methanol,
ethyl acetate, DMSO, DMF and acetonitrile solutions respectively to
explore the fluorescence emission of probe L. As shown in Fig. 1a, we
2+
regretted to find that the fluorescence changes of L on Zn and L on
2+
Mg were basically the same in the above solvents. Therefore, we chose
the ethanol that exhibited the strongest fluorescence after L combining
with metal ions as the solvent. And then we tried to add water into
ethanol to improve the selectivity of L to metal ions by changing the
polarity of the solvent [6]. As described in Fig. 1b, firstly, we tried to add
1
to obtain a pale yellow solid. Yield: 72.68 %; mp: 335–338 ℃. H NMR
(
400 Hz, DMSO-d
6
, TMS) δ
H
(ppm): 9.89 (s, 2 H), 8.88 (d, 1H, J =0.52
Hz,), 8.44 (q, 1H, J =1.76 Hz), 8.40 (d, 1H, J =7.72 Hz), 8.04 (d, 1H, J
7.4 Hz), 7.90 (m, 3 H), 7.75 (m, 2 H), 7.58 (m, 2 H), 7.07 (m, 1 H), 6.65
d, 2H, J =2.2 Hz), 6.49 (d, 2H, J =8.64 Hz), 6.43 (dd, 2H, J =8.68 Hz, J
2.28 Hz) (Fig. S1). 13C NMR (400 Hz, DMSO-d
, TMS) δ (ppm):
1
0 % water to ethanol, namely EtOH/H
2
O (10/1, V/V). Although the
=
2+
fluorescence intensity of Mg
decreased significantly, there still
(
2+
showed fluorescence that would interfere with the detection of Zn
.
=
6
C
Then, we tried to add 20 % water to ethanol, namely EtOH/H
2
O (5/1,
1
1
1
1
74.74, 164.50, 159.25, 153.29, 153.07, 152.66, 151.45, 140.84,
35.74, 134.79, 130.26, 129.68, 128.87, 128.62, 128.51, 128.22,
26.21, 124.32, 123.90, 123.53, 122.32, 120.38, 120.25, 120.00,
2+
V/V). In this solution, the fluorescence of Mg was almost quenched,
2+
but the fluorescence intensity of Zn was too low. Therefore, we found
2
that the most suitable solvent ratio EtOH/H O (9/1, V/V) within the
13.03, 110.25, 103.21, 65.65, 56.59, 19.08 (Fig. S3). ESI-MS calcu-
range of 10 %–20 % moisture content.
lated for [M+H] 553.1321, found 553.0766. [M + Na]+ 575.0566
+
(
Fig. S4).
Scheme 1. Reagents and conditions.
2

J. Sun et al.
Journal of Photochemistry & Photobiology, A: Chemistry 406 (2021) 113007
Fig. 2. UV–vis absorption spectra of L (50.0
μM) with gradual additional of
2
+
2
Zn (0.1-1.0 equiv.) in EtOH/H O (9/1, V/V).
2
+
Fig. 3. Fluorescence spectrum of L (50.0 M) in the presence of various metal
μ
Fig. 1. (a) Solvent effect on fluorescence intensity of the probe L, with Zn in
different solvent; (b) Fluorescence spectra of L in EtOH, upon increasing the
volume of water percentages from 1/10 to 1/5.
+
3+
2+
2+
2+
2+
3+
2+
3+
2+
ion (1.0 equiv.) of Ag , Al , Ba , Ca , Cd , Co , Cr , Cu , Fe , Hg ,
+
+
2+
2+
+
2+
2+
2+
K , Li , Mg , Mn , Na , Ni , Pb and Zn in EtOH/H
2
O (9/1, V/V). (λex =
4
28 nm, slit widths: 5 nm/3 nm).
3
.2. Absorption studies
In EtOH/H
2
the solution of EtOH/H O (9/1, V/V), L had excellent selectivity for
2
+
Zn
.
2
O solution (9/1, V/V), the UV–vis titration experiment of
L to Zn2 was carried out at room temperature. The titration spectrum
was shown in Fig. 2. In the absence of Zn2+, the solution of L displayed
+
In order to further explore the anti-interference ability of L with the
addition of Zn2 in this solution, the fluorescence spectrum was inves-
tigated in the presence of other metal ions (1.0 equiv). The results were
shown in Fig. 4. When different metal ions were added to the solution of
+
UV–vis absorption at 280 nm and 325 nm, which might be п-п* transi-
tions. And with the continuous addition of Zn2+, the color of the solution
L-Zn2 , most metal ions had little effect on the combination of L-Zn
+
2+
.
gradually darkened to yellow, the appearance of new absorption bands
at 400 nm, 425 nm and 450 nm might be due to n-п* transitions [39,40],
while the absorption peaks at 280 nm and 325 nm were fallen gradually.
And an isotopic site appeared at 364 nm, indicating that L and Zn2
2
+
Only the fluorescence emission intensity of Cu at 497 nm was signif-
2
+
icantly reduced [41]. It might be the magnetic properties of Cu that
led to the transfer of electrons and energy from the ligand to the metal
+
2
+
ion. In addition, it was worth mentioning that when Cu was added to
L, the color of L-Cu2 was also yellow. This result indicated that Zn
formed a complex.
+
2+
.3. Selectivity and competitiveness of L for Zn2+
was more dominant than most other competitive ions in the coordina-
3
tion complex with L.
The selectivity of L was analyzed by fluorescence spectroscopy, and
the effects of various metal ions on the properties of L were studied. As
shown in Fig. 3, under the excitation wavelength of 428 nm, L showed
3.4. Selectivity and competitiveness of L for Cu2
+
To explore the selectivity of the fluorescent probe L towards Cu2
+
,
almost no fluorescence emission at 497 nm in EtOH/H
2
O solution (9/1,
V/V), after addition of Zn2 , the significant fluorescence intensity was
enhanced. Furthermore, under the same conditions, the solution of L
after addition of other different metal ions exhibited hardly any fluo-
rescence emission at 497 nm. The experimental results suggested that, in
+
the UV–vis absorption spectroscopy experiment of L was conducted in
2
+
EtOH/H O solution (5/2, V/V) to avoid the interference of Zn . The
2
UV–vis spectrum of L combined with various metal ions was obtained
(Fig. 5). The spectrogram displayed that the absorption of L was
3

J. Sun et al.
Journal of Photochemistry & Photobiology, A: Chemistry 406 (2021) 113007
Fig. 4. Fluorescence intensity at 497 nm of L (50.0 M) before and after the
μ
2
+
Fig. 6. UV–vis absorption spectra of L (25.0
μ
M) before and after the addition
addition of Zn (1.0 equiv.) in the presence of various metal ion (1.0 equiv.) of
2
+
+
+
2
3+
+
2+
2+
2+
2+
2+
2+
3+
2+
3+
2+
+
+
2+
of Cu (1.0 equiv.) in the presence of various metal ion (1.0 equiv.) of Ag ,
Ag , Al , Ba , Ca , Cd , Co , Cr , Cu , Fe , Hg , K , Li , Mg
,
3
+
2+
2+
2+
2+
2+
2+
3+
2+
3+
2+
+
+
2+
2+
+
2+
Al , Ba , Ca , Cd , Co , Cr , Cu , Fe , Hg , K , Li , Mg , Mn ,
Mn , Na , Ni , Pb and Zn in EtOH/H
widths: 5 nm/3 nm).
2
O (9/1,V/V). (λex = 428 nm, slit
+
2+
2
Na , Ni , Pb and Zn in EtOH/H O (5/2,V/V).
Fig. 5. UV–vis absorption spectra of L (25.0
μ
M) in the presence of various
+
3+
2+
2+
2+
2+
3+
2+
3+
2+
metal ion (1.0 equiv.) of Ag , Al , Ba , Ca , Cd , Co , Cr , Cu , Fe
,
Fig. 7. Job’s plot for determining the stoichiometry between L and Zn in
EtOH/H
O (9/1, V/V). (λex = 428 nm, slit widths: 5 nm/3 nm).
2
+
+
+
2+
2+
+
2+
2+
2+
Hg , K , Li , Mg , Mn , Na , Ni , Pb and Zn in EtOH/H
2
O (5/2,V/V).
2
enhanced obviously at 427 nm and 453 nm after adding Cu2 (1.0
+
2+
concentration of Zn , a fluorescence titration experiment was con-
equiv), while L which was added other metal ions showed absorption at
ducted. We diluted probe L (5 mM) to 50
μ
M with a solution of EtOH/
2
+
2+
2
80 nm and 325 nm. To evaluate the competitiveness of Cu , we
H
2
O (9/1, V/V), and then dropped Zn (0.0–1.0 equiv) continuously to
2
+
continued to add Cu to the solution of L adding other metal ions. As
obtain a titration curve (Fig. 8). And in titration, it was so much fun to
shown in Fig. 6, the absorbances at 427 nm and 453 nm were increased
see that the fluorescence intensity of the probe L had a linear relation-
obviously after the addition of Cu2 , at the same time, the absorbances
at 280 nm and 325 nm were decreased. This result represented that Cu2
had priority over other metals in binding to L.
+
2+
ship with the concentration of Zn . The limit of detection (LOD) would
be calculated by the formula LOD = 3 / k ( : standard deviation of
blank sample, k: slope of linear relationship curve between fluorescence
+
σ
σ
intensity and Zn2 concentration). The detection limit of L to Zn was
+
2+
ꢀ 7
calculated to be 3.369 × 10 M (Fig. S5). According to the Benesi-
3
.5. Binding studies
Hildebrand formula, the correlation constant is:
2
+
.
The Job’s plot was used to verify the stoichiometry of L and Zn
1
1
1
F ꢀ Fm in
= K
a
(Fm ax ꢀ Fm in)[Zn2+]
+ F
m ax ꢀ Fm in
2
+
Keeping the total concentration of L and Zn
constant, the molar
2
+
fraction was [L] / [L + Zn ]. As shown in Fig. 7, the fluorescence in-
tensity reached the maximum value at 497 nm when the mole fraction
was 0.5. It could be concluded that stoichiometric ratio between L and
The meaning of the parameters mentioned in the above formula,
max, F and Fmin respectively represented the fluorescence intensity at
F
2
+
2
+
497 nm in the presence of saturated of Zn , various concentrations of
Zn was 1:1.
2
+
2+
Zn and L alone, K
a
was the binding constant of L with Zn . It was
2
+
4
concluded that the complex constant of Zn with probe L was 9.8 × 10
ꢀ
1
3
.6. Titration research
M
(Fig. S6). In addition, based on the data obtained from the UV–vis
2
+
spectrum titration experiment of L on Zn , we calculated the LOD as
In addition, to detect the binding ability between L and the
4

J. Sun et al.
Journal of Photochemistry & Photobiology, A: Chemistry 406 (2021) 113007
2
+
Fig. 8. Fluorescence spectrum of L (50.0
μ
M) with gradual titration of Zn (0-
2+
Fig. 9. UV–vis absorption spectra of L (25.0
μ
M) with gradual titration of Cu
1
.0 equiv.) in EtOH/H
2
O (9/1, V/V). (λex = 428 nm, slit widths: 5 nm/3 nm).
(
0.0-1.0 equiv.) in ethanol/water solution (5/2, V/V).
-
6
4
ꢀ 1
M (Fig. S8). The
2
.191 × 10 M (Fig. S7) and K
a
as 4.6193 × 10
results were basically consistent with the results calculated by the
fluorescence spectrum titration data.
Table 1
Comparison of probes for Zn /Cu detection.
2
+
2+
Similarly, to explore the binding ability between the concentration of
Recognition
Solvent (V/V)
EtOH/H O (95/5)
LOD/M
Reference
L and Cu2 , we conducted an ultraviolet titration experiment (Fig. 9).
+
2+
ꢀ 6
Zn
2
3.86 × 10
[32]
[47]
[48]
[49]
According to the ultraviolet titration spectrum, we linearly fitted the
Zn2+
CH CN/H O (1/1)
2.92 × 10ꢀ 7
3
2
2
+
2+
ꢀ 7
absorbance and the concentration of Cu . The detection limit (LOD) of
Zn
CH
3
CN
6 × 10
2
+
ꢀ 7
the probe L for Cu2 was calculated to be 5.3028 × 10 M by the
+
ꢀ 6
Zn
pH = 5.0 MES buffer containing 1 %
1.8 × 10
EtOH
formula LOD = 3
σ
/ k (Fig. S9). In addition, we could linearly fit 1 / (A -
2+
2+
2+
2+
ꢀ 7
ꢀ 5
ꢀ 6
ꢀ 8
Cu
Cu
Cu
Cu
HEPES-buffer
HEPES-buffer
1.6 × 10
[50]
[51]
[52]
[53]
2
+
Amin) and 1 / [Cu ] according to the Benesi-Hildebrand equation. It
1.5 × 10
2
+
can be concluded that the probe L had a complex constant of Cu of
2
H O
2.34 × 10
5
-1
1
.009 × 10
M
(Fig. S10). In addition, compared with previously re-
HEPES-buffer
8.9 × 10
2
+
2
+
2+
Zn
EtOH/H
EtOH/H
2
O (9/1)
3.369 ×
ported Zn and Cu fluorescent probes, the LOD values given here
were basically in the same range (Table 1).
ꢀ
0
7
1
This work
2
+
2.191 ×
Cu
2
O (5/2)
ꢀ 6
1
0
+
3
.7. Reaction mechanism of L to Zn2
The reaction mechanism of L to Zn2 seemed to be based on the
+
4. Conclusion
2
+
above-mentioned optical property experiment of L to Zn and the Job’s
plot. In the absence of Zn2+, the nitrogen atom of the fluorescein hy-
In brief, we designed and synthesized a new fluorescent probe L that
could detect Zn2 and Cu using fluorescein hydrazide and 4-oxo-4H-
+
2+
drazide [42,43] transferred an electron to 4-oxo-4H-benzo[h]methyl-
2
+
benzo[h]methylene-3-carbaldehyde as raw materials. Based on PET
ene-3-carbaldehyde to quench its fluorescence emission. When Zn was
added to L, the coordination of Zn2+ with the carbonyl oxygen atom of
2
+
mechanism, L could detect Zn with high selectivity. And the sensi-
2
+
tivity of L to Zn was higher than other ions. The detection limit of L for
the fluorescein hydrazide part, the oxygen atom of the 4-oxo-4H-benzo
2
+
ꢀ 7
Zn was only 3.369 × 10 M, which were basically in the same range
[
h]methylene-3-carbaldehyde part and the nitrogen atom of -C = N-
with the detection limits of the probes previously reported. Moreover,
inhibited this electron transfer process and strong fluorescence was
emitted, which was based on the photo-induced electron transfer (PET)
process [26,44–46]. As a result, intense fluorescence signal was
appeared at 497 nm (Scheme 2).
the high sensitivity and high selectivity of L to Zn2 was only obtained
+
+
by the fluorescence method. In addition, adding Cu2 to the solution of
the probe L in EtOH/H O (5/2, V/V) produced a visible color change
from colorless to yellow and a change in the ultraviolet-visible spectrum.
2
Similarly, L was more sensitive to Cu2 than other metal ions. The above
+
3
.7.1. Research on L as a solid probe
2
+
results showed that L could be used as a visual detection probe for Cu
and a fluorescence sensor for Zn2
In order to detect metal ions more quickly, we designed L as a solid
+
.
probe. Firstly, the cut filter paper was soaked in the EtOH/H
2
O (5:2, V/
V) solution of L (50 M) and dried it in air. Then, the various metal ion
μ
+
+
+
+
2+
2+
2+
2+
2+
2+
2+
CRediT authorship contribution statement
solution (Na , K , Ag , Li , Mg , Zn , Ba , Cu , Mn , Ni , Cd ,
2
+
2+
2+
2+
3+
3+
3+
Co , Pb , Hg , Ca , Al , Fe , Cr ) was taken by a clean dropper
2
+
Jie Sun: Conceptualization, Data curation, Formal analysis, Re-
sources, Methodology, Investigation, Software, Validation, Visualiza-
tion, Writing - original draft, Writing - review & editing. Tian-rong Li:
Project administration, Supervision. Cong Liu: Resources. Jia Xue:
Resources. Li-mei Tian: Resources. Kui Liu: Resources. Si-liang Li:
Resources. Zheng-yin Yang: Project administration, Funding acquisi-
tion, Supervision.
and dropped it on the filter paper, then Cu presented a yellow color
that was different from other metal ions, which could be observed with
the naked eye (Fig. 10). Handled the filter paper immersed in the EtOH/
2
H O (9:1, V/V) solution of L in the same way and placed it under a 365
nm UV lamp to observe the difference in luminescence (Fig. 11). Under
ultraviolet light, Zn2+ emitted obvious yellow-green fluorescence. Based
on the above experiments, we might be argued that L could be used as a
solid probe to detect Zn2 and Cu
+
2+
.
5

J. Sun et al.
Journal of Photochemistry & Photobiology, A: Chemistry 406 (2021) 113007
2
+
.
Scheme 2. Reaction mechanism of L on Zn
Fig. 10. The photograph of filter paper of L after addition of different metal ions under visible light.
Fig. 11. The photograph of filter paper of L after addition of different metal ions under 365 nm UV lamp.
Declaration of Competing Interest
We have no conflicts of interest to declare.
Acknowledgment
113007.
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