A photochromic diarylethene-functionalized fluorescent probe for Cd2+ and Zn2+ detections

Article abstract of DOI:10.1016/j.tet.2020.131618

A novel bifunctional chemosensor 1O constructed with diarylethene and pyridazine unit has been designed and synthesized with excellent photochromic properties upon UV/Vis radiation. The chemosensor 1O shows prominent selectivity and high sensitivity for Cd²⁺ and Zn²⁺ by obvious fluorescent enhancement with a low detection limit in water-acetonitrile solution (v_(water):v_{(acetonitrile)} = 1:9). The chemosensor 1O could be utilized as a fluorescent sensor for Cd²⁺ with a limit of detection (LOD) of 2.3 × 10^?6 M. With the presence of Zn²⁺, the fluorescence of the generated zinc complex enhances remarkably and the limit of detection (LOD) for Zn²⁺ is calculated to be 1.1 × 10^?5 M by Job's plot titrations. A logic circuit of this chemosensor 1O has been constructed with the input signals of UV and visible light, Cd²⁺ (or Zn²⁺) and EDTA and the output signal of the emission intensity. In addition, the concentrations of Cd²⁺ or Zn²⁺ in real water are detected quickly and conveniently by this chemosensor.

Full text of DOI:10.1016/j.tet.2020.131618

Tetrahedron 76 (2020) 131618
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A photochromic diarylethene-functionalized fluorescent probe for
Cd2þ and Zn2þ detections
Shanxi Peng, Junfei Lv, Gang Liu, Congbin Fan*, Shouzhi Pu**
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal University, Nanchang, 330013, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel bifunctional chemosensor 1O constructed with diarylethene and pyridazine unit has been
designed and synthesized with excellent photochromic properties upon UV/Vis radiation. The chemo-
sensor 1O shows prominent selectivity and high sensitivity for Cd2þ and Zn2þ by obvious fluorescent
enhancement with a low detection limit in water-acetonitrile solution (v(water):v(acetonitrile) ¼ 1:9). The
chemosensor 1O could be utilized as a fluorescent sensor for Cd2þ with a limit of detection (LOD) of
2.3 ꢀ 10ꢁ6 M. With the presence of Zn2þ, the fluorescence of the generated zinc complex enhances
remarkably and the limit of detection (LOD) for Zn2þ is calculated to be 1.1 ꢀ 10ꢁ5 M by Job’s plot ti-
trations. A logic circuit of this chemosensor 1O has been constructed with the input signals of UV and
visible light, Cd2þ (or Zn2þ) and EDTA and the output signal of the emission intensity. In addition, the
concentrations of Cd2þ or Zn2þ in real water are detected quickly and conveniently by this chemosensor.
© 2020 Elsevier Ltd. All rights reserved.
Received 7 June 2020
Received in revised form
10 August 2020
Accepted 4 September 2020
Available online 6 October 2020
Keywords:
Diarylethene
Cd2þ and Zn2þ
Fluorescence sensor
Logic circuit
Water sample
1. Introduction
diseases including prostate cancer [14], Alzheimer’s disease [15],
and diabetes [16]. The two elements noted above are in the same
With the development of industrialization, metal materials have
been used in various fields, such as architecture [1], manufacture
[2], transportation [3] etc. The accumulation of ions in environment
has broken the balance of ion concentrations in the ecosystem, and
the individual has been exposed to the environment which con-
tains a large amount of metal ions [4]. Cadmium, one of the most
dangerous heavy metals, can cause human arcinogenicity [5] and
toxicity [6], which has been widely utilized in many fields such as
agriculture, industry and metallurgy etc. Unfortunately, the bio-
accumulation of Cd2þ through the food chains can lead great threat
to human being and environment. The excessive intake of Cd2þ can
damage human organs such as liver and kidneys, and be relative to
cancer, cardiovascular diseases, heart disease, and diabetes [7e10].
As an essential element which has been found in the human body,
zinc, a secondary abundant transition metal in the Earth, takes part
in a wide variety of physiological and pathological processes, such
as regulators of gene expression, neural signal transmitters and
apoptosis [11e13]. Abnormal amount of zinc will lead to several
group [17], so they have similar physical and chemical features.
Therefore, exploration of highly selective sensors for Cd2þ and Zn2þ
will produce priceless value for human being.
Amounts of advanced methods including inductively coupled
plasma-atomic emission spectrometry (ICP-AES) [17], inductively
coupled plasma-mass spectrometry (ICP-MS) [18] and atomic ab-
sorption spectroscopy (AAS) [19] have been widely used for anal-
ysis of Cd2þ and Zn2þ. Compared to the methods discussed above,
fluorescent probes have the advantages of their easy operation,
high sensitivity, good selectivity and low cost [20e26], making
people explore the ionic sensors in the realm of chemistry and
biology. Among the reported fluorescent probes, diarylethene de-
rivatives showing prominent stability for heat and perfect anti-
fatigue character which could be used in ultimate condition and
transformed quickly [27e29] are the most promising candidates.
The diarylethene exists two formations of open-ring and closed-
ring, which are also identified as non-conjugated formation and
conjugated formation. Upon with the irritation of UV light, the
diarylethene can change from open-ring formation to closed-ring
formation, for the sake of the absorption wavelength becoming
longer and the absorption coefficient ascending. With the stimu-
lation of the identified ion, diarylethene molecule can undergo
poly-stable conversion [30]. The above properties could be used to
design multi-addressable switches. Although many chemosensors
* Corresponding author.
** Corresponding author.
E-mail addresses: fancb@jxstnu.edu.cn (C. Fan), pushouzhi@tsinghua.org.cn
(S. Pu).
https://doi.org/10.1016/j.tet.2020.131618
0040-4020/© 2020 Elsevier Ltd. All rights reserved.

S. Peng, J. Lv, G. Liu et al.
Tetrahedron 76 (2020) 131618
Scheme 1. The synthetic route and photochromism of 1O.
with the diarylethene units have been designed to recognize the
ions [31,32], the sensors based on diarylethene to detect Cd2þ and
Zn2þ of the same group have rarely been reported [33].
Quantum Yield Spectrometer QYC11347-11.
2.2. Synthesis of 1O
In recent decades, chemosensors with special selectivity and
high sensitivity for ion detections have been paid more and more
attentions due to their extensive applications, including environ-
mental pollution monitoring, medical diagnosis and mineral
exploration [34,35] etc. In this work, a novel chemosensor detector
for Cd2þ and Zn2þ, based on diarylethene and hydrazinylpyridazine
unit connected by Schiff structure, was designed and synthesized in
Scheme 1. Schiff base compounds with the lone pair electrons of
C]N bond which was a detective site for metal ions exhibited good
photochemical properties [36]. Besides, more nitrogen atoms were
introduced as chelating sites, such as pyridazine containing two
nitrogen atoms [37] and the photochromic diarylethene unit
bearing a pyridine unit. Expected as designed, the diarylethene
derivative 1O could detect Cd2þ and Zn2þ in water-acetonitrile
solution, with the emission intensity of this sensor dramatically
changing comparing alike other diarylethene fluorescence sensors
[38,39]. The data characterized by 1H NMR and 13C NMR to describe
the structure of 1O was drawn in ESI(Figure S1-S2). With the
stimulation of lights and chemical species, we carried out system-
ically the properties of its photochromism and fluorescence.
The synthesis route of 1-(2,5-dimethylthiophen-3-yl)-2-{2-
methylthiophen -5-[5-pyridinyl-2-(methylene)hydrazineyl-6-
chloropydidazin]-3-yl}perfluorocyclopentene(1O) was verified in
Scheme 1. Based on the reported method [37,38], compound 2 and
compound 3 were obtained.
2.2.1. Synthesis of compound 2
The compound 1 (2.0 g, 13.4 mmol) was dissolved in 50 mL 32%
ammonia water with a weak nitrogen flow at the same time, then
added hydrazine hydrate (4.3 g, 25%, 21.5 mmol). Stirring the
mixture was for 3 h at the reflux temperature. Then the reaction
was stopped, cooled into room temperature, and put into ice bath
with beige solids precipitated, and the precipitated was filtered and
vacuum dried to get compound 2 (1.5 g，10.42 mmol, yield 77.8%）.
1H NMR (DMSO-d6, 400 MHz),
d (ppm): 4.35 (s, 2H), 7.08 (d,
J ¼ 8.0 Hz, 1H), 7.41 (d, J ¼ 8.0 Hz, 1H),8.20 (s, 1H). The HRMS was
shown in Figure S3.
2.2.2. Synthesis of compound 1O
Diarylethene derivative 1O was constructed via the route in
Scheme 1. Compound 2 (0.05 g, 0.1 mmol) and compound 3
(0.014 g, 0.1 mmol) were dissolved in 10 mL absolute methanol, and
heated at reflux temperature for 12 h. Then the mixture was
descended to room temperature with light yellow power precipi-
tated. The precipitated was washed with methanol and dried to
obtain 1O (0.037 g, 0.06 mmol, yield 57.8%). 1H NMR (CDCl3,
2. Experiments
2.1. General procedures and materials
The solvents used in the experiments were analytic, and the
reagents purchased from reagent corporations were directly
applied. The salt solutions were prepared including HgCl2,
MnCl2$4H2O, Al(NO3)3$9H2O, Pb(NO3)2, KCl, Cd(NO3)2$4H2O,
400 MHz),
d (ppm): 1.88 (s, 3H), 1.97 (s, 3H), 2.43 (s, 3H), 6.73 (s,
1H), 7.34 (s, 1H), 7.43e7.45 (d, J ¼ 8.0 Hz, 1H), 7.71e7.74 (d,
J ¼ 12.0 Hz, 1H), 7.83e7.85 (d, J ¼ 8.0 Hz, 1H), 7.91e7.93 (d,
J ¼ 8.0 Hz, 1H), 8.79 (s, 1H), 8.20 (s, 1H),10.54 (s, 1H). 13C NMR
Ba(NO3)2,
Sr(NO3)2,
Cu(NO3)2$3H2O,
Ni(NO3)3$6H2O,
Zn(NO3)2$6H2O, Fe(NO3)3$9H2O, Cr(NO3)3$9H2O, Co(NO3)2$6H2O,
Ca(NO3)2$4H2O, Mg(NO3)2$6H2O. 1 mmol of inorganic ion was
weighted and dissolved in water to get the 10 mL. aqueous ionic
solution (0.1 M). The EDTA solution was made up by mixing
ethylene diamine tetraacetic acid disodium salt (Na2EDTA)
(0.2 mmol) and distilled water (2 mL).
(100 MHz, CDCl3)
d: 14.46, 14.68, 15.26, 116.51, 120.59, 124.28,
124.57, 124.81, 126.75, 129.34, 130.36, 132.96, 135.16, 137.98, 138.19,
139.96, 142.90, 146.53, 149.44, 152.67, 158.46.
3. Results and discussions
UVeVis spectra were measured with an Agilent 8453 UVeVis
spectrophotometer. Mass spectrometry analysis was operated on
an Agilent 1100 ion trap MSD spectrometer. 1H and 13C NMR spectra
were recorded on a Bruker AV400 (400 MHz) spectrometer using
DMSO-d6, CDCl3 and CD2Cl2 as the solvents and tetramethylsilane
(TMS) as the internal standard. Fluorescence spectra were collected
on a Hitachi Fe4600 fluorescence spectrophotometer. Infrared
spectra (IR) were recorded on a Bruker Vertexe70 spectrometer.
The fluorescence quantum yield was measured with an Absolute PL
3.1. Photochromism and fluorescent properties of 1O
The photochromic properties of 1O, at the concentration of
2.0 ꢀ 10ꢁ5 M, were studied in water-acetonitrile (v:v ¼ 1:9) at room
temperature in Fig. 1A. The maximum absorption peak of 1O was
observed at 358 nm (ε ¼ 5.2 ꢀ 104 molꢁ1 L cm ꢁ1) due to the
p-p*
transition [40]. The absorption peak at 358 nm would descend upon
the irritation with 297 nm light. Meanwhile, a new absorption peak
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S. Peng, J. Lv, G. Liu et al.
Tetrahedron 76 (2020) 131618
Fig. 1. Diarylethene derivative 1O (A) ultraviolet absorption spectrogram. and color change of solution (B) the change of emission intensity.
at 569 nm (ε ¼ 1.2 ꢀ 104 molꢁ1 L cmꢁ1) appeared, accompanied
with the color changing from colorless to purple owing to the
photocyclization of 1O to 1C. Reached the photostationary state
(PSS), three isosbestic points had been observed at 260 nm, 300 nm,
377 nm respectively, which exhibited a reversible photochromic
reaction of two components. Upon irritation with visible light
tendency of emission peak had ended. With the emission decrease
of ca. 62.9%, the diarylethene derivative exhibited high fluorescent
modulation efficiency. The residual fluorescence of PSS told the fact
that the diarylethene 1O did not completely react into 1C.
Contrarily, the cyclization 1C, stimulated by visible light
(l > 500 nm), completely regenerated into open-ring isomer 1O,
(
l
> 500 nm), the absorption peak changed totally from closed-ring
and the color would be recovered.
1C to open-ring 1O with the color fading from purple to colorless.
The quantum yields of open ring ɸo-c was 0.005, compared with 1,2-
bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene.
3.2. The ions detection of diarylethene 1O
In Figure S4, the water-acetonitrile (v:v ¼ 1:9) solution of dia-
rylethene 1O, at room temperature, was lighted by the alternating
UV/Vis light to examine the anti-fatigue properties. The result
provided that the diarylethene derivative 1O degraded at the rate of
23.75% after open and close ring 10 times.
The fluorescent properties of 1O were also determined in the
water-acetonitrile (v:v ¼ 1:9) solution. The emission peak at
444 nm of 1O was observed with 380 nm light irradiation in Fig. 1B.
Upon irritation with 297 nm light, the emission intensity of 1O
descended remarkably, because the new isomer 1C with non-
fluorescence was appeared [41]. The PSS reached, the descending
In order to investigate the response of 1O to various metal ions
including Kþ, Ba2þ, Hg2þ, Sr2þ, Cr3þ, Fe3þ, Mg2þ, Mn2þ, Ca2þ, Ni2þ
,
Pb2þ, Sn2þ, Co2þ, Cu2þ, Cd2þ and Zn2þ, they were added respec-
tively in water-acetonitrile solution (v:v ¼ 1:9) to observe the
alternation of emission peak intensity and fluorescent color. As
shown in Fig. 2, excited by the 380 nm UV light, the emission peak
intensity and fluorescent color of 1O remarkably changed. When
5.0 equiv. Cd2þ were added, the fluorescence of 1O at 482 nm was
enhanced greatly, and the fluorescent color turned from dark to
cyan. Meanwhile, when 5.0 equiv. Zn2þ was added, the fluorescence
of 1O at 493 nm was enhanced remarkably and the color altered
Fig. 2. Diarylethene derivative 1O at the water-acetonitrole solution (v:v ¼ 1:9) (A) the emission intensity stimulated by different metal ions; (B) selectivity of bar chart for metal
ions; (C) emission color after adding different ions.
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S. Peng, J. Lv, G. Liu et al.
Tetrahedron 76 (2020) 131618
Fig. 3. Diarylethene derivative 1O at the water-acetonitrole solution (v:v ¼ 1:9) altered by Cd2þ (A)absorption spectra and color change of 1O (B) absorption spectra and color
change of 1C.
from dark to orange yellow. The change stimulated by other ions
would not be observed with naked eyes in Fig. 2B. The enhance-
ment of emission intensities contributed to this reason that diary-
lethene 1O combined with Cd2þ or Zn2þ respectively to form
1OeCd2þ(1O’) complex or 1OeZn2þ(1O00) complex. The result
manifested that the diarylethene derivative 1O could be viewed as
a fluorescent sensor for Cd2þ and Zn2þ with eminent selectivity in
Fig. 2C.
increased with the peak at 358 nm descending as the complex
1OeCd2þ(1O’) appeared, and the color of the solution turned from
colorless to pale brown. The quantum yield of 1O’ was 0.040. As the
excessive EDTA was added into 1O’ solution, the state of solution
recovered to the primary state as it was shown in Fig. 3A. Accom-
panied with the addition of excessive Cd2þ into 1C solution, the
solution altered from purple to pale brown due to the decrease of
the absorption peak at 371 nm and the increase of the absorption
peak at 408 nm. Shown in Fig. 3B, the color of 1CeCd2þ(1C’) would
recover to the initial state with the excessive addition of EDTA.
The photochromic properties of 1O’ were further studied. As is
shown in Fig. 4, the compound of 1O’, lighted by ultraviolet light at
297 nm, appeared a new absorption peak at 581 nm which would
be increased gradually with the passage of irritation going on. As
reached the PSS, two absorptive points were observed at 355 nm
and 421 nm, respectively. The closed-ring isomer 1C’ would be
produced at the same time, and the color of solution altered from
yellow to brown. By contrary, the solution of 1C’, stimulated by
3.3. The features of 1O toward Cd2þ
With the addition of Cd2þ, the absorption peak at 403 nm slowly
visible light (l > 500 nm), changed gradually to open-ring isomer
1O’, and the color of solution altered from brown to dark yellow.
With the accumulation of Cd2þ ions, the fluorescent titration
experiment would be studied at the water-acetonitrile solution
(v:v ¼ 1:9) of the compound 1O (2.0 ꢀ 10ꢁ5 mol Lꢁ1) at the room
temperature to obtain the change of fluorescent spectrum. As
shown in Fig. 5A, with the addition of Cd2þ into the water-
acetonitrile solution of 1O, the emission peak shifted red gradu-
ally from 442 nm to 485 nm and the emission intensity ascended
with the increase of Cd2þ. The emission intensity would continue to
become higher until the concentration of Cd2þ was added to the 3.6
equiv, with the emission peaks altering from 471 nm to 485 nm.
Fig. 4. Ultraviolet absorption spectrum and color change of 1O′at the water-
acetonitrile solution (v:v ¼ 1:9) lighted by UV/Vis.
Fig. 5. Diarylethene derivative 1O at the water-acetonitrile solution (A) emission intensity and fluorescent color with the addition of Cd2þ or EDTA (B) titration cure of 1O added
Cd2þ and linear relationship between emission intensity and the concentrations of Cd2þ
.
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S. Peng, J. Lv, G. Liu et al.
Tetrahedron 76 (2020) 131618
Fig. 8. Anti-interference experiment and error bars of it between 1O (2.0 ꢀ 10ꢁ5 M) at
the water-acetonitrile solution and different metal ions (5.0 equiv.) Black Blank: 1O
and different metal ions; Red Blank.
Fig. 6. Fluorescent switch of 1O’ at the water-acetonitrile solution (v:v ¼ 1:9).
Continuing to add the Cd2þ ion, the emission intensity would not
change. A new complex 1OeCd2þ (1O’) would be produced with
the fluorescent color of the solution altering from dark to cyan.
Excessive EDTA added into the solution of 1OeCd2þ (1O’), the
fluorescent spectrum and fluorescent color would recover to the
initial state, which indicated that EDTA could dissociate the Cd2þ
from 1O’. Further, the relationship between Cd2þ and emission
intensity was studied in Fig. 5B. The result indicated that the
emission intensity was positively correlated with the concentration
of Cd2þ at a certain concentration range. Thus, the complex 1O
The anti-interference experiment was operated at the room
temperature to examine fluorescent selectivity of 1O toward
various metal ions (5.0 equiv. of 1O) such as Ca2þ, Sn2þ, Kþ, Pb2þ
,
Mg2þ, Cr3þ, Co2þ, Hg2þ, Mn2þ, Fe3þ, Cu2þ, Ba2þ, Ni2þ, Agþ, Al3þ, Sr2þ
in water-acetonitrile solution. When the Cd2þ(5.0 equiv.) ion was
added into 1O solution coexisted with various metal ions, the
emission intensity was enhanced by Sn2þ and Ba2þ, also quenched
by Co2þ, Cu2þ, Ni2þ in Fig. 8. The results showed that most metal
ions did not interfere the detection of Zn2þ and Cd2þ, except the
could be considered as a chemosensor to detect the ion of Cd2þ
.
metal ions of Co2þ, Cu2þ and Ni2þ
.
The emission intensity of 1O’ was further studied. As verified in
Fig. 6, upon the irritation with ultraviolet at 297 nm, the emission
intensity of 1O’ at 501 nm descended gradually, and the fluorescent
color of solution became dark yellow from orange. When reached
the PSS, the emission peak intensity decreased from 411.8 to 203.2,
along with the formation of closed-ring 1C’. Correspondingly, when
3.4. The characters of 1O toward Zn2þ
As shown in Figure S5A, when the ion of Zn2þ was added in the
solution of 1O, the absorption peak at 358 nm would be descended,
and a new peak at 403 nm would occur with the reason of the
formation of complex of 1OeZn2þ(1O00) whose quantum yield was
0.029. With the increase of Zn2þ, the new peak would ascend until
the 16 equiv. ion of Zn2þ was added. Two clear isosbestic points
were observed at 314 nm and 382 nm at the same time, accom-
panied with the color changing from colorless to dark yellow. Then,
when excessive EDTA was added into the 1O00 solution, the solution
could recover to initial state. When 16 equiv. Zn2þ was added into
the 1C solution, the color turned from purple to earthy yellow in
Figure S5B, with the reason that the absorption peaks at 371 nm
descended and 576 nm ascended. The 1CeZn2þ(1C00) solution
would recover to the state of 1C after the addition of excessive
EDTA.
exposed to visible light (l > 500 nm), the formation of closed-ring
1C’ would recover to the formation of open-ring 1O.
Furthermore, the fluorescent titration experiment was studied
at the room temperature to investigate the relation between the
water-acetonitrile of 1C and Cd2þ. As shown in Fig. 7, the Cd2þ ion
was added into the water-acetonitrile solution of 1C on the drop-
wise. The emission peak intensity, changing with the addition of
Cd2þ, would ascend gradually with red shift. After Cd2þ was added
2.1 equiv., the emission peak intensity got the maximum, and the
excessive Cd2þ did not make the intensity change. Red-shift of the
emission peak altered from 445 nm to 500 nm in accompany with
the color becoming dark cyan from dark. After addition of excessive
EDTA, the fluorescent peak intensity and color recovered to the
statement of 1C.
The photochromic properties of 1O00 were further studied. Upon
the irritation of 297 nm light, the 1O00 solution altered to the closed-
ring isomer 1C00 with a new absorption peak at 581 nm, and the
color changed from dark yellow to brown with naked-eye obser-
vation. Using the stimulation of visible light (l > 500 nm), com-
pound 1C00 totally altered to open-ring isomer 1O00, with the color
changing to yellow in Figure S6.
When the solution of Zn2þ was added into the water-acetonitrile
solution of 1O on the drop-wise, the emission peak of 1O at the
state of open-ring shifted red gradually with the enhancement of
peak. The emission peak intensity, altered from 422 nm to 498 nm,
reached the top, as the Zn2þ was added at the concentration of 4.8
equiv. shown in Figure S7A. With the complex 1OeZn2þ(1O00)
generating, the color of the solution became orange yellow from
dark. After adding excessive EDTA in 1O00 solution, the fluorescent
spectrum and fluorescent color recovered to 1O. The result was
further analyzed that at a certain concentration rang the emission
Fig. 7. Fluorescent switch of 1C′at the water-acetonitrile solution (v:v ¼ 1:9).
5

S. Peng, J. Lv, G. Liu et al.
Tetrahedron 76 (2020) 131618
intensity at 486 nm was linear with the concentration of Zn2þ in
and Cd2þ or Zn2þ in the water-acetonitrile solution (v:v ¼ 1:9). As
shown in Fig. 9A, when the molar ratio of [Cd2þ]/([Cd2þ]þ[1O])
reached the point of 0.5, the emission intensity got the top, which
showed that the combination ratio between compound 1O and
Cd2þ was 1:1. Meanwhile, the association constant (Ka) between 1O
and Cd2þ in the water-acetonitrile solution (v:v ¼ 1:9) was
1.7 ꢀ 104 molꢁ1 L (R ¼ 0.99439) [42] in Fig. 9B by the equation of
Benesi-Hildebrand. Based on the method reported above, the limit
of detection for Cd2þ could reach 2.3 ꢀ 10ꢁ6 mol Lꢁ1 [42] in Fig. 9C.
Similarly, Figure S11A manifested the stoichiomical relation be-
tween 1O and Zn2þ in the water-acetonitrile solution (v:v ¼ 1:9)
would be obtained by the Job’s plot. With the alteration of molar
ratio of [Zn2þ]/([Zn2þ]þ[1O]) achieving the point of 0.5, the emis-
sion intensity ascended on the top, exhibiting that the stoi-
chiomecal ratio between 1O and Zn2þ was 1:1. Based on the
equation of Benesi-Hildebrand noted above, the association con-
stant (Ka) between the 1O and Zn2þ in the water-acetonitrile so-
lution (v:v ¼ 1:9) was 4.9 ꢀ 103 molꢁ1 L(R ¼ 0.99103) in
Figure S11B. The limit of detection (LOT) for Zn2þ could reach
1.1 ꢀ 10ꢁ5 mol Lꢁ1 demonstrated in Figure S11C.
Figure S7B. The results discussed above proved that complex 1O
could be considered as a chemosensor for Zn2þ
.
The emission peak intensity of complex 1O00 decreased steadily
when stimulated by ultraviolet light. Reaching PSS, the emission
peak intensity descended from 174.4 to 106.6 because of the new
formation of closed-ring 1O00. The color of the solution altered from
orange to dark yellow in Figure S8. Exposed to the visible light
(l
> 500 nm), the emission peak intensity of 1C00 could recover to
the initial statement.
The fluorescent titration experiment, depicted in Figure S9, was
carried out in the water-acetonitrile solution of 1C adding Zn2þ ion
on the drop. As the addition of Zn2þ into the water-acetonitrile of
1C, the emission peak shifted to higher with the enhancement of
intensity. The peak reached the maximum, as the addition of Zn2þ
reached 4.0 equiv., with the formation of complex 1CeZn2þ(1C00).
The color of solution became dark yellow from dark. After the
excessive EDTA was added, the fluorescent color and the emission
intensity returned to the original.
Ca2þ, Kþ, Pb2þ, Cr3þ, Ba2þ, Co2þ, Sn2þ, Mn2þ, Fe3þ, Mg2þ, Cu2þ
,
Agþ, Ni2þ, Al3þ, Sr2þand Hg2þ were added into the solution of 1O to
examine the interference of them with the detection of Zn2þ ion. As
shown in Figure S10., when Zn2þ (5.0 equiv.) was added into 1O
solution containing various metal ions, the emission intensity was
increased by Cd2þ, quenched by Co2þ, Cu2þ, Ni2þ, and inhibited by
In order to further research the binding formation, the ESI-MS,
titration experiments and IR spectra of 1O, 1O’ and 1O00 were
operated. The 1 : 1 coordination stoichiometry of 1O with Cd2þ or
Zn2þ was further confirmed by the ESI mass spectrometry (ESI-MS)
analysis (Figure S12). As shown in Figure S12A, a characteristic peak
at 849.7 m/z for [Cd2þþ1Oþ2NOꢁ3 -Hþ] (calcd 850.4) was observed.
Fe3þ
.
Meanwhile, Figure S12B manifested
a characteristic peak at
799.8 m/z which was for [Zn2þþ1Oþ2NOꢁ3 -Hþ] with the calculation
of 800.4. 1H NMR titration experiments were done in CDCl3 to
investigate the binding mode of 1O with Cd2þ or Zn2þ. A new peak
at 4.692 appeared as shown in Figure S13., when Cd2þ ion was
3.5. Mechanism of 1O to Cd2þ and Zn2þ
The Job’s plot of UVeVis titration of 1O toward Cd2þ and Zn2þ
was put forward to further elucidate the interaction between 1O
Fig. 9. Diarylethene derivative 1O at the water-acetonitrile solution (v:v ¼ 1:9) (A) the complex ration and linear relationship between 1O and Cd2þ (B) association constant and
linear relationship of association constant between 1O and Cd2þ (C) LOD and linear relationship of 1O for Cd2þ
.
6

S. Peng, J. Lv, G. Liu et al.
Tetrahedron 76 (2020) 131618
added. In order to exclude the influence of water, deuterium oxide
was titrated in the solution of 1O. As few deuterium was added, a
new peak at 4.692 appeared in Figure S14, which indicated that the
new peak was the peak of deuterium oxide and Cd2þ ion did not
influence the shift of 1O. After the addition of Zn2þ ion to the 1O
solution, a new peak at 4.692 was examined shown in Figure S15,
and as the addition of deuterium oxide a new peak at 4.692 was
also observed in Figure S14. This phenomenon also showed that the
new peak was the peak of deuterium oxide and Zn2þ ion did not
influence the shift of 1O. In addition, IR spectrum was carried out to
detect the binding sites shown in Figure S16. After adding the ions
of Cd2þ or Zn2þ respectively, a new peak at 2400 cmꢁ1 appeared,
manifesting that a triple bind would form. According to what had
been discussed above, the binding mode between 1O and Cd2þ or
Zn2þ was verified in Scheme 2.
operated. The method that was used to measure the contents of
Cd2þ or Zn2þ in actual water was reported [43,44]. Water samples
were filtered with 0.2 mm membranes to filter the precipitation.
Then, different contents of Cd2þ or Zn2þ were added in the actual
water sample to prepare different concentration gradients. In order
to compare the experimental data, the parallel testes were carried
out. The ions of Cd2þ or Zn2þ were dissolved into deionized water to
prepare samples with the concentrations similar to the actual
concentrations before and determine the standard curve. Fluores-
cence of the two samples in the corresponding gradient was
investigated, and the actual value was calculated by comparing the
two data of same concentrations. One sample was conducted three
times and calculated the average data, and the Recover (%), RSD (%)
and Relative error (%) were obtained. The results were shown in
Table 1 and Table 2.
3.6. The practical application
3.6.2. Application for logic gate
Discussed the properties of the diarylethene derivative above,
the fluorescent emission intensity could be effectively adjusted by
Cd2þ (or Zn2þ)/EDTA and UV/Vis light in water-acetronitrile
3.6.1. The detection of actual water
The application of 1O to detect the ions of Cd2þ or Zn2þ was
Scheme 2. Photochromism, color and fluorescence alteration of 1O stimulated by Cd2þ/Zn2þ and UV/Vis lights.
7

S. Peng, J. Lv, G. Liu et al.
Tetrahedron 76 (2020) 131618
Table 1
Concentration of Cd2þ in practical samples.
Sample
Cd2þ spiked (
m
mol Lꢁ1
)
Cd2þ recovered (
m
mol Lꢁ1
)
Recover（%）
RSD（%）
Relative error（%）
Yao Lake
6
6.02
100.33
101.70
100.06
97.83
101.30
98.88
2.51
4.28
1.82
3.01
3.11
2.37
0.33
1.7
0.0625
ꢁ2.17
1.3
ꢁ0.1125
10
16
6
10
16.0
10.17
16.01
5.87
10.13
15.82
Tap Water
Table 2
Concentration of Zn2þ in practical samples.
Sample
Zn2þ spiked (
m
mol Lꢁ1
)
Zn2þ recovered (
m
mol Lꢁ1
)
Recover（%）
RSD（%）
Relative error（%）
Yao Lake
6.0
5.93
9.95
15.93
5.99
9.98
16.01
99.83
99.50
99.56
99.83
99.80
100.06
3.56
3.65
2.32
1.04
2.25
1.01
ꢁ1.17
ꢁ0.5
10.0
16.0
6.0
10.0
16.0
ꢁ0.438
ꢁ0.17
ꢁ0.2
Tap Water
ꢁ0.0625
Fig. 10. Logic circuits constructed by 1O and the symbols: In1 (UV light), In2 (visible light), In3 (Zn2þ or Cd2þ), In4 (EDTA).
solution to create a logic gate (Fig. 10). The four input signals were
at 485 nm (or 498 nm) was the output signal. When the emission
intensity was 2-fold enhancement than the original state, output
signal could be looked up as ‘on’ with a Boolean value of ‘1’.
In1: 297 nm UV light, In2:
l
> 500 nm visible light, In3: Cd2þ (or
Zn2þ), and In4: EDTA, and the fluorescent emission intensity of 1O
Table 3
Table of all possible strings of four binary-input data and the corresponding output digit.
Input
Output
InA (UV)
InB (Vis)
InC(Zn2þorCd2þ
)
InD (EDTA)
l
em ¼ 498 nm or 485 nm
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
1
0
0
1
0
0
1
0
0
1
1
0
1
1
0
1
1
0
0
0
1
0
0
1
0
1
0
1
1
0
1
1
1
0
0
0
0
1
0
0
1
0
1
1
0
1
1
1
1
0
0
0
1
0
0
0
0
1
0
0
1
0
0
0
0
8

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Tetrahedron 76 (2020) 131618
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Otherwise, it was thought as ‘off’ state with a Boolean value of ‘0’.
Stimulated by those four signals, the diarylethene derivative 1O
presented on-off-on colorimetric switchable behavior. Taking
strings of ‘0, 0, 1, and 0’ for instance, they relate to input signals of
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Similarly, different operations could get various outputs. All
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A novel diarylethene with pyridazine unit, showing high
sensitivity and selectivity for Cd2þ and Zn2þ in water-acetonitrile
(v:v ¼ 1:9), was designed and synthesized. In addition, the appli-
cations of logic gate and the detection of Cd2þ or Zn2þ in real water
were realized by the novel diarylethene fluorescent sensor. These
works would be beneficial to the researchers of fluorescent sensors
based on diarylethene unit.
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.
Acknowledgments
The authors are grateful for the financial support from the Na-
tional Natural Science Foundation of China (21861017, 41867053)
the key project of Natural Science Foundation of Jiangxi Province
(20192ACBL20011).
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2020.131618.
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9