A diarylethene derived Fe3+ fluorescent chemosensor and its application in wastewater analysis

Article abstract of DOI:10.1016/j.jphotochem.2019.112282

A diarylethylene derivative containing an acylhydrazone Schiff base moiety was designed and synthesized. Upon alternative irradiation with UV and visible lights, the compound showed distinct fluorescence switching properties based on fluorescence resonance energy transfer mechanism. On the other hand, the fluorescence can be efficiently quenched by 69 fold in the presence of Fe³⁺ ion in methanol. As a Fe³⁺ fluorescent chemosensor, the sensing mechanism, the influence of pH on sensing properties, and the practical application were also studied. In the complex, the breaking of the intramolecular H-bonding between the –CO [dbnd] NH– proton and the oxygen at the C[dbnd] O of lactone, the weaking of electrons transfer, and the paramagnetic nature of Fe³⁺ induced a consequent decrease fluorescence. The compound was found to be stable in a wide range of pH and a highly efficient Fe³⁺ ion quencher with a detection limit of 4.6 × 10^?6 mol L^?1. Moreover, the fluorescent detection of Fe³⁺ was demonstrated by filter paper strips. A series of test papers with different Fe³⁺ concentrations were prepared and used as the standard card. The analytical application of measuring Fe³⁺ concentration in wastewater samples were evaluated by comparison with the standard card directly and quickly.

Full text of DOI:10.1016/j.jphotochem.2019.112282

Journal Pre-proof
A diarylethene derived Fe3+ fluorescent chemosensor and its application
in wastewater analysis
Yongjie Li, Wenhao Pan, Chunhong Zheng, Shouzhi Pu
PII:
S1010-6030(19)31733-2
DOI:
https://doi.org/10.1016/j.jphotochem.2019.112282
JPC 112282
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27 November 2019
2 December 2019
Please cite this article as: Li Y, Pan W, Zheng C, Pu S, A diarylethene derived Fe3+ fluorescent
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Photobiology, A: Chemistry (2019), doi: https://doi.org/10.1016/j.jphotochem.2019.112282
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A diarylethene derived Fe3+ fluorescent chemosensor and its
application in wastewater analysis
Yongjie Li, Wenhao Pan, Chunhong Zheng* and Shouzhi Pu*
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal
University, Nanchang 330013, PR China
*Corresponding author: ezirobot@163.com, (C. Zheng), pushouzhi@tsinghua.org.cn (S. Pu),
Tel/Fax.: +86-791-83831996.
Graphical abstract
A diarylethylene derivative containing an acylhydrazone Schiff base moiety was designed and
synthesized, and its sensing for the Fe3+ ion was studied. The fluorimetric test paper for Fe3+ were
prepared and could be used to measure Fe3+ concentration in wastepaper by comparison with the
standard card.
1

Highlights

A diarylethylene derivative containing an acylhydrazone Schiff base moiety was designed
and synthesized.


The derivative showed a selective and fluorescence changes upon addition of Fe3+.
The sensing for Fe3+ was well demonstrated by the standard card, which can be evaluated
Fe3+ concentrations directly and quickly.
Abstract
A diarylethylene derivative containing an acylhydrazone Schiff base moiety was designed
and synthesized. Upon alternative irradiation with UV and visible lights, the compound showed
distinct fluorescence switching properties based on fluorescence resonance energy transfer
mechanism. On the other hand, the fluorescence can be efficiently quenched by 69 fold in the
presence of Fe3+ ion in methanol. As a Fe3+ fluorescent chemosensor, the sensing mechanism, the
influence of pH on sensing properties, and the practical application were also studied. In the
complex, the breaking of the intramolecular H-bonding between the CO=NH proton and the
oxygen at the C=O of lactone, the weaking of electrons transfer, and the paramagnetic nature of
Fe3+ induced a consequent decrease fluorescence. The compound was found to be stable in a wide
6
1
range of pH and a highly efficient Fe3+ ion quencher with a detection limit of 4.6 × 10 mol L .
Moreover, the fluorescent detection of Fe3+ was demonstrated by filter paper strips. A series of
test papers with different Fe3+ concentrations were prepared and used as the standard card. The
analytical application of measuring Fe3+ concentration in wastewater samples were evaluated by
comparison with the standard card directly and quickly.
Keywords: Photochromism; Diarylethene; Acylhydrazone Schiff base; Fluorescent chemosensor;
Fe3+ ion sensing; Test strip
2

1. Introduction
Ion ion (Fe3+), as one of the biologically important metal ions, plays an essential role in
synthesizing a series of enzymes involved in oxygen uptake, oxygen metabolism, and electron
transfer [1,2]. Imbalanced Fe3+ levels seriously affect the normal activities of organisms [3]. High
concentrations in the body will lead to the imbalance between oxidation and antioxidation which
damage DNA and induced mutation [4−6]. And deficiency will cause anaemia and related
discrepancies such as impaired cognitive function, lethargy, low immunity [7]. Fe3+ can also cause
potential health hazards through the food chain due to its migration and enrichment in the
environment in environment water system [8]. Therefore, the development of reliable and
sensitive chemosensor for the monitoring of the Fe3+ is highly desirable. In recent decades, a rapid
advancement in analytical technology for metal ion is optical chemosensors. Among them,
fluorescence sensors have attracted much attention due to its low detection levels, high selectivity
and sensitivity and ease of operation [9]. So far, a large variety of fluorescence sensors have been
designed based on various identification mechanisms, such as PET [10], FRET [11], ICT [12,13],
and ESIPT [14] etc. Although most of them showed highly selective recognition of a particular ion
and meet the specific recognition function, there are very few fluorescent sensors for Fe3+ ions.
Thus, a highly selective fluorescent chemosensor for Fe3+ is an immediate required.
Diarylethene, as one of the photochromic molecules, has two different molecular forms. They
are characterized by a reversible transformation between the open-ring and closed-ring forms with
distinct absorption spectra upon alternative irradiation with UV and visible light [1518]. Most
diarylethene molecules are not appreciably fluorescent on their own, but combining them with a
fluorophore has been used to modulate the fluorescence [19,20]. Coumarin group was frequently
chosen as the fluorophore due to its excellent spectroscopic properties, light stability and less
toxicity [21]. When a suitable receptor was attached to the fluorophore, a desired chemosensor
would be constructed by fluorescence change mechanism [22]. Both N and O atoms are frequently
the donor atoms, which readily combine with transition metal cations such as Cu2+ [23], Co2+ [24],
Fe3+ [25], Zn2+ [26]. Usually, diarylethenes-based chemosensors were conducted by combining a
diarylethene core and an appending functionalized fluorophore by different reaction such as
aldimine condensation [27], Click chemistry [28], Willimson chemistry [29], Heck chemistry [30],
3

etc. Among them, aldimine condensation is the most commonly strategy due to its easily
synthesize, high yields. Until now, despite of all these efforts being devoted to the
diarylethene-based chemosensors containing a salicylidene Schiff base group [31], seldom
fluorescent and colorimetric sensors for Fe3+ have been achieved.
Herein, a diarylethene derivative (1o) containing an acylhydrazone Schiff base moiety was
designed and synthesized. Experiments showed that 1o showed evident absorption spectral and
emission spectral changes upon alternative irradiation with UV and visible lights. More
importantly, Fe3+ could selectively and sensitively control the fluorescence of 1o. The structure,
the isomer transformation in the presence of light and Fe3+ are shown in Scheme 1.
Scheme 1. The structure, photochromism of 1o and sensing for Fe3+.
2. Experimental
2.1 General methods
Chemical reagents were purchased from either Alfa or TCI and can be used without further
purification. Solvents were obtained from Beijing Chemical Plant. Anhydrous solvents were of
spectroscopic quality and purified by distillation prior to use. All solution-phase reactions were
carried out under dry argon atmosphere. Reactions were monitored by analytical thin-layer
chromatography on plates coated with 0.25 mm silica gel 60 F254 (Qingdao Haiyang Chemical).
Melting points were measured with a WRS-1B melting point apparatus. Infrared spectra were
recorded on a Bruker Vertex70 spectrometer. The fluorescence quantum yields were measured by
Perkineimer lambea 750 UV/vis. NMR spectra were obtained on a Bruker AV400 spectrometer
4

with tetramethyl silane (TMS) as internal reference and CDCl3 as solvent. Absorption spectra were
obtained with an Agilent 8454 UV/vis spectrometer. Fluorescence spectra were studied in a
Hitachi F-4600 fluorescence spectrophotometer. Photoirradiation was carried out with an
SHG200 UV lamp, a CX21 ultraviolet fluorescence analysis cabinet, and a BMH250 visible
lamp. Light of appropriate wavelengths was isolated by light filters. The measurements of pH
values were recorded on a PHS3C pH meter (Shanghai, China).The metal ions were prepared by
dissolving their their respective salts (0.20 mmol) in distilled water (2 mL). Aqueous solutions of
Ag+, Ba2+, Cu2+, Zn2+, Cd2+, Mn2+, Fe3+, Pb2+, Ca2+, Co2+, Cr3+, Ni2+, Mg2+, Sn2+, and Al3+ were
prepared using their corresponding nitrates, and K+, Hg2+ were prepared using their corresponding
chlorides.
2.2. Synthesis
Compound 3 was prepared by reacting 2 with N2H4·H2O in methanol, which was further
condensated with 4 [32] to yield compound 1o. The synthesis of 1o was illustrated as shown in
Scheme 2.
Scheme2. The synthesis route of 1o.
2.2.1 Synthesis of 7-diethylamino-3-hydrazide-coumarin (3)
According to the previous procedure [33], to
a
stirred solution of ethyl
7-(diethylamino)coumarin-3-carboxylate (1.0 g, 3.5 mmol) in 20 ml absolute ethanol, hydrazine
hydrate (1 mL, 20.4 mmol) was injected at room temperature, the mixture was refluxed for
overnight. The system was cooled down to room temperature, and subsequently filtered off and
washed with cold ethanol. The produce was recrystallized from ethanol to give yellow solid at a
yield of 82%. 1H NMR (400 MHz, CDCl3): δ (ppm) 1.24 (t, 6H, CH3, J = 8.0 Hz), 3.46 (m, 4H,
CH2, J = 8.0 Hz), 4.16 (s, 2H, NH2), 6.48 (s, 1H, phenyl-H), 6.65 (d, 1H, phenylH, J = 8.0 Hz),
5

7.43 (d, 1H, phenylH, J = 8.0 Hz), 8.67 (s, 1H, =CH), 9.73 (s, 1H, NH); 13C NMR (CDCl3,
100 MHz), δ (ppm): 11.41, 44.09, 95.62, 107.25, 108.15, 109.02, 130.12, 146.98, 151.69, 156.62,
161.07, 162.84.
2.2.2
Synthesis
of
1-(2-methyl-3-benzothiophenyl)-2-{2-methyl-5-[4-(7-diethylamino
coumarinhydrazide)-phenyl]-3-thienyl}perfluorocyclopentene (1o)
To a stirred solution of compound 4 (0.105 g, 0.2 mmol) in 10 mL ethanol, compound 3
(0.041g, 0.2 mmol) was added. The mixture was refluxed for 6 h and no compound 4 was detected
by thin-layer chromatography silica gel plate. A yellow solid was obtained with 85% yield by
1
vacuum evaporating the solvent. M.p. 452453 K. H NMR (400 MHz, CDCl3): δ (ppm) 1.26 (t,
6H, CH3, J = 8.0 Hz), 1.96 (s, 3H, CH3), 2.31 (s, 3H, CH3), 3.48 (m, 4H, CH2, J = 8.0 Hz),
6.53 (s, 1H, phenylH), 6.69 (d, 1H, phenylH, J = 8.0 Hz), 7.22 (s, 1H, thiopheneH), 7.31–7.34
(t, 1H, phenylH, J = 6.0 Hz), 7.37–7.38 (d, 1H, phenylH, J = 4.0 Hz), 7.44 (d, 2H, phenylH, J
= 8.0 Hz), 7.49 (d, 1H, phenylH, J = 8.0 Hz), 7.58 (d, 1H, phenylH, J = 7.8 Hz), 7.74–7.76 (d,
1H, phenylH, J = 8.0 Hz), 7.77 (s, 1H, phenylH), 7.79 (s, 1H, phenylH), 8.17 (s, 1H, Hc), 8.86
(s, 1H, Hb), 11.92 (s, 1H, Ha; 13C NMR (CDCl3, 100 MHz), δ (ppm): 11.41, 13.84, 17.42, 19.29,
44.19, 57.47, 95.60, 107.63, 107.95, 109.30, 119.26, 121.08, 122.24, 123.53, 123.97, 124.35,
124.49, 127.40, 130.44, 132.28, 133.91, 137.22, 140.05, 141.34, 141.49, 146.60, 148.21, 152.00,
156.84, 158.89,161.81; IR (ν, KBr, cm-1): 3058 (NH), 1697 (C=O), 1617 (C=N), 1385 (COC);
)
LRMS (ESI m / z: [M  H], calcd, 778.2; found, 778.0.
3. Results and discussion
3.1 Photochromism properties of 1o
The photochromic behavior of 1o with stimulation UV and visible lights in methanol (1.0 ×
5
1
10 mol L ) at room temperature was studied. As shown in Fig 1A, the absorption spectrum of
1o in methanol exhibits absorption bands at 226, 262, 337 and 440 nm. The maximum absorption
at 440 nm is due to the 7-N,N'-diethylamine coumarin-3-hydrazide-1-benzaldehyde Schiff base
(reference) (Fig. S1), which has a maximum absorption at 433 nm. The photochromic core
decreased the electron-donating ability of the shiff base moiety within 1o, which enhanced the
degree of intramolecular charge transfer (ICT).Thus, a 7 nm red-shift was observed. Consistently,
6

the red-shifted behavior (2 nm) was also observed in the fluorescence emission spectrum of 1o
(Fig. S2). Upon irradiation with 297 nm light, the peaks at 226, 262, 337, and 440 nm were little
changed due to these absorption peaks overlapped that of coumarin derivative. The absorption
coefficient of 7-N,N'-diethylamine coumarin-3-hydrazide-1-benzaldehyde Schiff base is similar to
that of 1o, indicating that most of the absorption of 1o at 440 nm is due to the 7-N,N'-diethylamine
coumarin-3-hydrazide-1-benzaldehyde Schiff base. Little of the absorbed photons by 1o can be
used for the photocyclization reaction. A new absorption peak at 554 nm appeared due to the
formation of the closed-ring isomer 1c accompanied by an immediate color change from yellow to
dark yellow. When the photostationary state was arrived, three clear isosbestic points were
observed at 269, 323 and 360 nm, indicating a two-component photochromic reaction process
[34]. Upon irradiation with visible light (> 510 nm), the dark yellow color faded and the
absorption spectrum returned to the initial state of 1o
.
The presence of a 7N(C2H5)2 group and 3CONHN=CHbenzene group at the coumarin
fluorophore in 1o induced the transfer of electrons within the molecule, like a push-pull system
[35]. Thus, compound 1o alone displays a strong and single fluorescence emission band at
506 nm with a fluorescence quantum yield (Ф = 0.13), when excited at 395 nm. The
intramolecular H-bonding stabilization between the CO=NH proton and the oxygen at the C=O
of lactone also enhanced the fluorescence [36]. As most of the reported diarylethenes [37], 1o
exhibited a relatively strong fluorescence switch, as shown in Fig 1B. Upon irradiation with 297
nm light, the emission intensity gradually decreased. When the photostationary state was arrived,
the emission intensity of 1o was quenched to ca. 29.64%. This was ascribed to the formation of
the closed-ring isomer of 1c, accompanied by the fluorescence resonance energy transfer (FRET)
[38]. The emission band of the 7-diethylamino coumarinhydrazide unit 3 was 494 nm (430–650
nm), and the absorption peak of the colosed-ring isomer of the photochromic core 4 was 548 nm
(450–670 nm) (Fig. S3). The emission band of 3 well overlaps with the absorption wave range of
the colosed-ring isomer of diarylethene 4, which is helpful for the FRET. Thus, upon irradiation
with 297 nm light, the energy was transferred from the excited 7-diethylamino coumarinhydrazide
unit to the photochromic core 4, accompained by the fluorescence quenching. Reversely, the
fluorescence of 1o could be restored upon irradiation with appropriate visible light (λ > 510 nm).
7

(A)
(B)
Fig. 1. (A) Absorption spectral and color changes of 1o upon alternating irradiation with UVvis
light in methanol (1.0 × 105 mol L-1); and (B) Fluorescence spectral and color changes of 1o upon
alternating irradiation with UVvis light in methanol (1.0 × 105 mol L-1).
3.2 Detection of Fe3+ in methanol
The metal ions recognition of 1o was studied by fluorescence spectroscopy. As shown in Fig.
2A, addition of 10 equiv. of metal ions (Fe3+, Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Pb2+,
5
K+, Mg2+, Ca2+, Ba2+, Sn2+ and Al3+) to 1o in methanol (1.0  10 mol L-1) induced major
quenching of fluorescence intensity for Fe3+ due to the formation of 1oFe3+ complex. Compared
with the free 1o, the fluorescence quantum yield was decreased by 69 fold (ΦFe = 0.04, ΦFe / Φ0 =
69). Moreover, for the co-existence of Fe3+ ion and other ions, the fluorescence intensity was
similar to that in the presence of only Fe3+, as shown in Fig. 3. The result indicated a highly
selective response of 1o for Fe3+ as compared to the other metal ions.
(A)
8

(B)
Fig. 2. (A) Fluorescence spectral of 1o in methanol (1.0  105 mol L-1) upon addition of 10 equiv.
of various metal ions; and (B) Fluorescent photos of 1o with various metal ions.
Fig. 3. Responses of 1o in methanol (1.0  105 mol L-1) to various anions. Red bars represent the
addition of 10 equiv. various anions to the solution of 1o. Black bars represent the addition of 10
equiv. Fe3+ to the above solution, respectively.
The changes in the e emission intensity of 1o with the different Fe3+ concentrations at room
temperature was shown in Fig. 4A. With the addition of changeable amounts of Fe3+, the emission
intensity at 506 nm gradually decreased. When 11 equiv. of Fe3+ was added, 1o opened a
nonradiative deactivation channel induced by paramagnetism with an unfilled d shell. The binding
of Fe3+ and 1o initiated a charge transfer, which inhibited the electron transfer with 1o, causing
28% fluorescence quenching [39].. The interaction between 1o and Fe3+ could occur at C=O of
lactone, and –NH, which could be identified as binding to transition and post transition metals
[40]. Job’s plot was carried out to determine the binding stoichiometry of 1o with Fe3+. As shown
in Fig. 4B, the intensity of the system with themolar ratio of Fe3+ for a series of solutions, in which
the total concentration of 1o and Fe3+ was kept constant. Feature point appeared at 0.5 on the
abscissa, indicating a 1 : 1 stoichiometry between 1o and Fe3+. Using the fluorescence titration
data, the 1 : 1 stoichiometry between 1o and Fe3+ was further confirmed by the Benesi–Hildebrand
9

equation, as shown in Fig. 4C. The association constant (Ka) was calculated to be 1.49 × 105 mol-1
L by using the Benesi–Hildebrand equation. The detection limit of Fe3+ was obtained by plotting a
graph between the relative emission intensity at 506 nm as a function of the Fe3+ constrations.
1
Based on 3σ / S, the limit of detection of 1o for Fe3+ was 4.6 × 10-6 mol L (Fig. 4D). Compared
with the recently reported Fe3+ sensors (Table 1), 1o has relatively high association constant and
low limit of detection. Moreover, the emission intensity of 1oFe3+ could completely returned to
that orginal state 1o upon adding of EDTA, which demonstrated that 1o sensed Fe3+ reversibly.
The coordination-dissociation cycles can be repeated four times (Fig. S4).
(A)
(B)
(C)
(D)
Fig. 4. (A) Fluorescence spectral changes and fluorescence titration of 1o upon addition of Fe3+
(011 equiv.) in methanol (1.0  105 mol L-1), (B) Job’s plot showing the 1:1 complex of 1o with
Fe3+, and (C) HildebrandBenesi plot based on the 1:1 binding stoichiometry, and (D) The limit of
detection (LOD) for Fe3+ with 1o.
Table 1. Comparative study of analytical performance of 1o with the recently reported sensors for
Fe3+.
10

Detection
limit
Association
constant
Structure
Approaches
Fluorescent
Ref.
Media
(mol L-1)
THF/H2O
(6/4, v/v)
2.2 × 104
9.8 × 104
6
7
3.73 × 10
7
6
1.09 × 10
EtOH/H2O
(2/8, v/v)
Fluorescent
Fluorescent
4
THF/H2O
(6/4, v/v)
1.54 × 10
1.74 × 10
1.05 × 10
100
3
33
5
Fluorescent
Colorimetric
8.8 × 103
4.0 × 105
5
5
H2O
(pH=7.4)
Fluorescent
Colorimetric
Tris–HCl buffer
medium
Present
work
1.49 × 105
Fluorescent
6
4.6 × 10
Methanol
By adding Fe3+, the emission intensity of 1c peaked at 506 nm also decreased about 68%, as
shown in Fig. 5. The result was consistent with the interaction between Fe3+ and 1o. The
closed-ring isomer 1c had equal capability of recognition of Fe3+ compared to the open-ring
isomer 1o. The sensing Fe3+ of 1c was also reversible. Moreover, the complex 1oFe3+ showed
fluorescence switch changes upon alternating irradiation with UVvis light, as shown in Fig. S5.
The fluorescent modulation efficiency was 66%, which is higher than that of 1o.
11

5
1
Fig. 5. Fluorescence spectral changes and color changes of 1c in methanol (1.0  10 mol L ) in
the presence of Fe3+.
3.3 pH studies
The dependence of emission intensity of the 1o and its Fe3+ complex on the pH of the mediun
were studied in the pH range of 3.011.0 at 1o (1.0 × 105 mol-1 L), Fe3+ in methanol. As shown in
Fig. 6, the emission intensities of 1o were high and remained almost constant in the pH range of
3.011.0. After mixing 1o with Fe3+, the emission intensity decreased at all pH values, and
remained constant in the range of 3.011.0. These data showed that 1o can be used to detect Fe3+
in a wide range of pH including at physiological pH.
Fig. 6. Fluorescence emission intensity of 1o in methanol solution vs pH before and after addition
of 11 equiv. Fe3+. The pH of the solutions was adjusted by addition of 0.1 mol L-1 HCl (or 0.1 mol
L−1 NaOH).
3.4 Possible binding mechanism of 1o to Fe3+
12

To gain a clear understanding of the possible binding mode of 1o with Fe3+ , the low
resolution mass spectrometry (LRMS) and FT-IR analysis were employed. The peak at m/z 981.0
+
was assignable to [1o + Fe3+ + 2 NO3 + Na  H] (m/z calcd: 981.1), that verified the complex
formation. As shown in Fig. S6, a band at around 3058 cm-1 could be assigned to the –NH group
of hydrazide group. In the complex spectrum, the peak disappeared which indicated that the
hydrazide involved the complexation. At the same time, the band at around 2696 cm-1 decreased
and the peak at 1513 cm-1 became narrower. The band of Schiff base (C=N) appeared as a single
band at 1617 cm-1 in the spectrum of 1o, which was not affected by adding Fe3+. Moreover, the
band showed a clear distinction at 1385 cm-1 after addition of Fe3+ suggesting the participation of
carbonyl of the lactone (C=O) group. These observations revealed that Fe3+ binding with 1o was
mainly through the nitrogen at the imine moiety and the oxygen atom at the carbonyl of the
lactone (C=O) group. The possible structure of the 1o-complex was shown in Scheme 1.
3.5 Practical Application

3.5.1 Fluorimetric test paper strip measurement
To investigate the practical application of the fluorimetric sensor, test strips measurement
were conducted. First, the Whatman filter papers were immersed into the methanol solution of 1o
1
(0.001 mol L ), then drying them at room temperature [41,42]. As shown in Fig. 7A, the
fluorescence color change of test strips soaked with 1o from green to cyan was immediately
observed after dropwise addition of Fe3+, wherease, other interfering metal ions (Cr3+, Mn2+, Co2+,
Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Pb2+, K+, Mg2+, Ca2+, Ba2+, Sn2+ and Al3+) did not produce an
obvious fluorescence color change.
Therefore, 1o would be very useful for the fabrication of sensing devices with fast and
convenient detection of Fe3+ ions. On the other hand, with the increase of Fe3+, the fluorescence
4
color of test strips soaked with 1o changed from green to indigo even in the presence of 1.0  10
1
mol L of Fe3+, as shown in Fig. 7B. The minimal concentration of Fe3+ detectable of the 1o test
4
1
papers was 1.0  10 mol L .
13

Fig. 7. (A) Photographs of test strips for detecting various anions including Cr3+, Fe3+, Mn2+, Co2+,
3
Ni2+, Cu2+, Zn2+, Cd2+, Hg2+, Pb2+, K+, Mg2+, Ca2+, Ba2+, Sn2+ and Al3+ in methanol (1.0 × 10
1
mol L ), and (B) Standard card for Fe3+ concentration detection in an wastewater sample.
3.5.2 Practical application to water samples
As a fluorescent sensor, 1o was further studied for determination of Fe3+ in tap water and the
Ganjiang river water by standard addition method [43]. Both the water samples were filtered three
times through a 0.2 mm membrane filter, then were spiked with a given amount of Fe3+, and
finally analyzed by using familiar procedures. As shown in Table 2, the recovery for Fe3+ was
from 92.7 to over 105.5 %. Therefore, 1o can be used to detect the spiked Fe3+ with the
satisfactory recovery.
Table 2. Detection of Fe3+ in environmental water samples.
Tap water
Ganjiang River
Spiked
Recovered
Recovery
(%)
Spiked
Recovered
Recovery
(%)
(μmol L-1)
(μmol L-1)
(μmol L-1)
(μmol L-1)
9.0
9.49
10.20
12.87
105.45
92.75
98.98
9.0
8.83
11.02
13.51
98.15
100.21
103.89
11.0
13.0
11.0
13.0
14

15.0
14.51
96.73
15.0
13.81
92.09
4. Conclusion
A diarylethene derivative containing a photochromic core and an acylhydrazone Schiff base
moiety was successfully synthesized, which provided a photochromic FRET system. The
compound exhibits the fluorescence from the coumarin-3-hydrazide-1-benzaldehyde Schiff base,
which was readily modulated upon alternative irradiation with UV and visible lights. On the other
hand, a strong fluorescence quenching was observed upon addition of Fe3+. A pH titration showed
that 1o had stable fluorescence property over a wide pH range of 3.011.0, which suggests that 1o
is suitable for application under physiological conditions. Moreover, the fluorimetric test paper
strips soaked with 1o was prepared which could showed highly selective for sensing Fe3+. Based
on the standard card, the Fe3+ in water samples can be detected conveniently.
We declare that we do not have any commercial or associative interest that represents a conflict of
interest in connection with the work submitted. The manuscript entitled “A diarylethene derived
Fe3+ fluorescent chemosensor and its application in wastewater analysis”.
We declare that we do not have any commercial or associative interest that represents a conflict of
interest in connection with the work submitted.
Acknowledgments
The authors are grateful for the financial support from the National Natural Science Foundation of
China (41867053), the “5511” science and technology innovation talent project of Jiangxi
(2016BCB18015), the key project of Natural Science Foundation of Jiangxi Province
(20171ACB20025), the Project of Jiangxi Science and Technology Normal University Advantage
Sci-Tech Innovative Team (2015CXTD002), the Project of the Science Funds of Jiangxi
Education Office (GJJ180621), and the Open Project Program of “311 high level engineering
center”, Jiangxi Science and Technology Normal University (KFGJ18004).
15

Appendix
For Fig. S1 to Fig. S9, please refer to supplementary information.
16

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