A highly selective fluorescent chemosensor for Cu2+ based on a diarylethene with a 2,1,3-benzoxadiazole unit

Article abstract of DOI:10.1002/poc.3839

A novel photochromic diarylethene containing a 2,1,3-benzoxadiazole structure has been synthesized and its multicontrollable fluorescence properties have been systematically studied by the stimulation of light and metal ions. The compound exhibited favora

Full text of DOI:10.1002/poc.3839

Received: 31 October 2017
DOI: 10.1002/poc.3839
Revised: 13 December 2017
Accepted: 3 February 2018
R E S E A R C H A R T I C L E
2
+
A highly selective fluorescent chemosensor for Cu based
on a diarylethene with a 2,1,3‐benzoxadiazole unit
Zhihui Zhang | Hongliang Liu
| Shouzhi Pu
Jiangxi Key Laboratory of Organic
Chemistry, Jiangxi Science and
Technology Normal University,
Nanchang, China
Abstract
A novel photochromic diarylethene containing a 2,1,3‐benzoxadiazole structure
has been synthesized and its multicontrollable fluorescence properties have
been systematically studied by the stimulation of light and metal ions. The
compound exhibited favorable photochromism and fluorescent switching
properties. Furthermore, it can serve as a fluorescent chemosensor for highly
Correspondence
Shouzhi Pu, Jiangxi Key Laboratory of
Organic Chemistry, Jiangxi Science and
Technology Normal University, Nanchang
2+
selective recognition of Cu in aqueous acetonitrile. When triggered by
330013, China.
2+
Email: pushouzhi@tsinghua.org.cn
Cu , it displayed a remarkable blue shift from 594 to 524 nm (70 nm) with a
significant fluorescence color change from yellow to bright green. As a result,
a logic circuit has also been constructed on the basis of light and chemical
stimulation.
Funding information
Innovation fund of graduate student,
Grant/Award Number: YC2016‐X03; Sci-
ence Funds of Jiangxi Science & Technol-
ogy Normal University, Grant/Award
Number: 2016XJZD003; Science and
Technology Innovation Talent Project of
Jiangxi Province, Grant/Award Number:
KEYWORDS
2+
benzoxadiazole, Cu recognition, diarylethene, fluorescent chemosensor, logic circuit
20165BCB18015; Science Funds of Natural
Science Foundation of Jiangxi Province,
Grant/Award Numbers: 20171BAB213018
and 20171ACB20025; National Natural
Science Foundation of China, Grant/
Award Number: 21662015
1
| INTRODUCTION
samples are highly meaningful for human health and
[
17,18]
environmental protection.
Considering the importance of Cu , in the past few
years, number of analytical methods such as
2+
In the human body, copper is the third most abundant
essential micronutrient followed by iron and zinc.
[
1–6]
It
a
is the highest concentration in the liver and brain and
colorimetric method, atomic absorption spectroscopy,
inductively coupled plasma mass spectrometry, and
[7–9]
plays a vital role in neurons.
However, at higher
concentration levels, it will damage proteins, nucleic
electrochemical method have been reported for their
[10]
[3,19–23]
acids, and lipids
and cause a wide variety of symptoms
determination.
However, these methods are not
2+
such as nausea, diarrhea, stomach cramps, and neurode-
suitable for online monitoring of Cu because of their
low selectivity, need for expensive instruments, and
delayed responses. Compared with other techniques,
[11–13]
generative disorders.
Furthermore, a considerable
accumulation of copper will cause serious environmental
pollution and disrupt natural ecosystems, especially in
fluorescent probes exhibit great advantages such as high
[
14–16]
[24,25]
drinking water.
monitoring of Cu
Hence, selective detecting and
in biological and environmental
selectivity and sensitivity.
Fluorescent chemosensors
2+
have distinct advantages in terms of sensitivity, selectivity,
[
26]
response time, real‐time analysis, and easy operation.
2+
Thus, the design and synthesis of fluorescent Cu probes
Zhihui Zhang and Hongliang Liu contributed equally to this work.
has received intense attention.
J Phys Org Chem. 2018;e3839.
wileyonlinelibrary.com/journal/poc
Copyright © 2018 John Wiley & Sons, Ltd.
1 of 11
https://doi.org/10.1002/poc.3839

2
of 11
ZHANG ET AL.
SCHEME 1 Photochromism of diarylethene 1O
+
Until now, a large number of fluorescent sensors
respective metal nitrates in distilled water, except for K ,
2+
2+
2+
2+
for Cu
reported.
have been designed, synthesized, and
Ba , Hg , and Sn (all of their counter ions were
chloride ions). Ethylene diamine tetraacetic acid (EDTA)
(0.1 mol/L) was obtained by the dissolution of EDTA
[27–29]
[30–32]
Among these reported sensors
for
2+
recognition of Cu , diarylethenes are very promising
molecular because of their remarkable fatigue resistance,
thermal stability and multiresponsively photoswitchable
properties under various stimulations (UV and visible
disodium salt (Na EDTA) (0.2 mmol) in distilled water
2
(2 mL).
Nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker AV400 spectrometer by using
tetramethylsilane (TMS) as an internal standard and with
[33–35]
[
UV/vis] lights and chemical substances).
Nowadays,
many reports on diarylethene‐based fluorescent
2
+
[36–39]
chemosensors for Cu have been published.
For
dimethyl sulfoxide (DMSO) and CD CN as the solvent.
3
[39]
example, Fu
has synthesized
diarylethene for Cu with a 1,8‐naphthalimide Schiff base
a
photochromic
Mass spectra were obtained on a Bruker AmaZon SL
spectrometer. Elemental analysis was measured by a PE
CHN 2400 analyzer. Melting point was measured on a
WRS‐1B melting point apparatus. Absorption spectra
were measured using an Agilent 8453 UV/vis spectropho-
tometer. Photoirradiation was conducted using an MUL‐
165 UV lamp and an MVL‐210 visible lamp. The required
wavelength was isolated by the use of appropriate filters.
Fluorescence spectra were measured using a Hitachi
F‐4600 spectrophotometer with 5‐nm slit for both excita-
tion and emission.
2+
unit. However, these chemosensors mostly show fluores-
2+
cence quenching when triggered by Cu , which are easy
to be disturbed by other factors in environment. Further-
more, fluorescent chemosensors with Stokes shift can
effectively avoid interference from other factors of environ-
ment. In this condition, it is of great significance to synthe-
2+
size a fluorescent chemosensor for Cu that displays a
remarkable Stokes shift of fluorescence emission.
In this paper, we designed and synthesized a novel fluo-
2+
rescent chemosensor for Cu with a 2,1,3‐benzoxadiazole
[40–44]
structure. 2,1,3‐Benzoxadiazole
provides a novel
2.2 | Synthesis of the target compound
sensing approach for fluorometric detection of metal ions
[
45–50]
as a probe in the environmental analytical fields.
The diarylethene not only acted as a fluorescent sensor
The synthetic route for the target diarylethene, 1‐(2‐
methyl‐5‐phenyl‐3‐thienyl)‐2‐{2‐methyl‐5‐[4‐(4‐2,1,3‐
2
+
for detection of Cu with high selectivity and sensitivity
but also afforded a multiaddressable switch for the
construction of logic circuit because of its fluorescence
benzoxadiazole)
aminemethyl]‐phenyl‐3‐thienyl}
perfluorocyclopentene (1O) was shown in Scheme 2.
The compound 2 were facilely synthesized in high
yield according to the similar procedures by previous
2+
was well controlled by UV/vis lights and Cu . The
photochrimism of the diarylethene was shown in
Scheme 1.
[
51–53]
reported methods.
2
.3 | Synthesis of 1‐(2‐methyl‐5‐phenyl‐3‐
2
2
| EXPERIMENTAL
.1 | General methods
thienyl)‐2‐[2‐methyl‐5‐(4‐formylphenyl)‐3‐
thienyl] perfluorocyclopentene (3)
Compound 2 (4.45 g, 7.50 mmol) and p‐toluenesulfonic
acid (1.49 g, 8.63 mmol) were dissolved in a mixture of
water (30 mL) and acetone (120 mL). Pyridine (0.68 g,
8.63 mmol) was added into the mixture followed by
refluxing overnight at 350 K. The reaction was cooled to
room temperature. The mixture was then washed sequen-
tially with aqueous NaHCO3 and water. After being
The solvents were analytical reagent and were purified by
standard methods prior to use such as distillation. All of
the reagents for the synthesis of the target compound
were purchased from various commercial sources and
used without further purification. The solutions of metal
ions (0.1 mol/L) were prepared by the dissolution of their

ZHANG ET AL.
3 of 11
SCHEME 2 Synthetic route of diarylethene 1O
13
extracted with ethyl acetate, the organic layer was dried
over Na SO , filtered, and concentrated. The crude prod-
(d, J = 8.0 Hz, 1H) (Figure S3); C NMR (DMSO,
100 MHz), δ (ppm): 14.0, 62.5, 122.1, 122.5, 125.0, 125.3,
127.1, 128.1, 129.2, 130.9, 132.5, 140.8, 141.2, 141.7,
141.8, 142.7 (Figure S4).
2
4
uct was purified by column chromatography on silica gel
using petroleum ether/ethyl acetate (v/v = 8:1) as eluent
to afford 3.70‐g compound 3 as a blue solid in a 90% yield.
1
M.p. 374‐375 K; H NMR (DMSO, 400 MHz, TMS), δ
(
7
2
ppm): 2.00 (s, 3H), 2.02 (s, 3H), 7.34 (t, J = 8.0 Hz, 1H),
2.5 | Synthesis of 1‐(2‐methyl‐5‐phenyl‐3‐
thienyl)‐2‐[2‐methyl‐5‐(4‐
.43 (t, J = 8.0 Hz, 2H), 7.51 (s, 1H), 7.64 (d, J = 8.0 Hz,
H), 7.76 (s, 1H), 7.89 (d, J = 8.0 Hz, 2H), 7.95 (d,
bromomethylphenyl)‐3‐thienyl
perfluorocyclopentene (5)
13
J = 8.0 Hz, 2H), 10.01 (s, 1H) (Figure S1); C NMR
DMSO, 100 MHz), δ (ppm): 14.0, 14.1, 122.5, 124.9,
(
1
1
To a stirred anhydrous CH Cl (50 mL) of compound 4
2
2
25.3, 125.7, 128.2, 129.2, 130.4, 132.5, 135.3, 137.9,
40.2, 141.3, 141.8, 143.2, 192.3 (Figure S2).
(
(
1.65 g, 3.00 mmol) was added methanesulfonyl chloride
0.40 mL, 4.80 mmol), triethylamine (0.75 mL, 5.40 mmol)
with vigorous stirring in the ice‐water bath. After stirring
for 5 minutes at 273 K, 10‐mL anhydrous tetrahydrofuran
containing LiBr (1.04 g, 12.00 mmol) was added and the
reaction mixture was stirred for 30 minutes at this temper-
ature. The reaction was warmed to room temperature and
stirred for 12 hours. The product was extracted with
CH Cl . The organic layer was washed with saturated
2
.4 | Synthesis of 1‐(2‐methyl‐5‐phenyl‐3‐
thienyl)‐2‐[2‐methyl‐5‐(4‐
hydroxymethylphenyl)‐3‐thienyl]
perfluorocyclopentene (4)
To a stirred solution of compound 3 (2.74 g, 5.00 mmol) in
2
2
tetrahydrofuran (50 mL), NaBH (0.23 g, 6.00 mmol) was
sodium bicarbonate and water then dried over Na SO ,
2 4
4
added and continuously stirred. After refluxing for
filtrated, and evaporated. The crude product was purified
by column chromatography on silica gel using the mixture
solvent of petroleum ether and ethyl acetate (v/v = 20:1) as
the eluent to obtain compound 5 (1.47 g, 2.40 mmol) as
1
0 hours, the mixture was cooled to room temperature
and quenched with water. The mixture was extracted with
CH Cl , dried over anhydrous Na SO , filtered, and evap-
2
2
2
4
1
orated. The residue was purified by chromatography on
silica gel using the mixture solvent of petroleum ether
and ethyl acetate (v/v = 3:1) as the eluent to give 4
blue solid in 80% yield. M.p. 369‐370 K; H NMR (DMSO,
400 MHz, TMS), δ (ppm): 1.99 (s, 3H), 4.76 (d,
J = 20.0 Hz, 1H), 7.34 (t, J = 8.0 Hz, 1H), 7.43 (t,
J = 8.0 Hz, 1H), 7.49 (s, 1H), 7.50 (s, 1H), 7.54 (s, 1H),
(
3
1
2.53 g, 4.60 mmol) as a blue solid in 92% yield. M.p.
20‐321 K; H NMR (DMSO, 400 MHz, TMS), δ (ppm):
.99 (s, 6H), 4.52 (d, J = 4.0 Hz, 1H), 5.24 (s, 1H), 7.34
1
13
7.62 (s, 1H), 7.64 (s, 1H) (Figure S5); C NMR (DMSO,
100 MHz), δ (ppm): 14.0, 34.0, 122.5, 123.0, 124.9, 125.1,
125.3, 125.5, 126.1, 127.2, 128.1, 129.2, 129.7, 130.2, 132.5,
132.6, 141.1, 141.2, 141.5, 141.7 (Figure S6).
(t, J = 8.0 Hz,1H), 7.38 (s, 1H), 7.43 (t, J = 8.0 Hz, 1H),
7
.47 (s, 1H), 7.50 (s, 1H), 7.59 (d, J = 8.0 Hz, 1H), 7.63

4
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ZHANG ET AL.
2
.6 | Synthesis of 1‐(2‐methyl‐5‐phenyl‐3‐
J = 8.0 Hz, 2H), 7.68 (s, 1H), 7.89 (t, J = 6.0 Hz, 1H)
13
thienyl)‐2‐{2‐methyl‐5‐[4‐(4‐2,1,3‐
benzoxadiazole)aminemethyl]‐phenyl‐3‐
thienyl} perfluorocyclopentene (1O)
(Figure S7); C NMR (DMSO, 100 MHz): δ (ppm): 14.0,
45.7, 100.0, 101.6, 122.4, 122.6, 125.0, 125.3, 125.4, 127.9,
128.1, 129.2, 131.2, 132.5, 135.1, 136.1, 138.9, 141.0,
1
41.2, 141.6, 141.7, 144.7, 149.8 (Figure S8); MS (ESI):
−
Compound 5 (0.31 g, 0.50 mmol) and 6 (0.07 g, 0.50 mmol)
m/z 666.1[M‐H] (calc. 667.1) (Figure S9).
were dissolved in anhydrous CH CN (60 mL). Then,
3
K CO (0.28 g, 2.00 mmol) and KI (0.08 g, 0.50 mmol)
2
3
were added, and the resulting mixture was refluxed at
53 K for 12 hours under an argon atmosphere. Subse-
3
3
| RESULTS AND DISCUSSION
3
quently, the reaction mixture was cooled to room temper-
ature, quenched with water, and the solvent was removed
under reduced pressure. After being extracted with
dichloromethane, the organic phase was dried over anhy-
drous Na SO , filtered, and evaporated. The crude
.1 | Photochromism and fluorescence
properties of 1O
The photochromic and fluorescence properties of 1O were
−
5
studied in acetonitrile (2.0 × 10 mol/L) at room temper-
ature. As shown in Figure 1A, the absorption maximum of
open‐ring isomer 1O was observed at 290 nm. Upon irradi-
ation with 297‐nm light, a new absorption band centered at
583 nm emerged because of the formation of the closed‐
ring isomer 1C with larger π‐electron delocalization in
the molecule, accompanied by a color change from col-
orless to blue. The colored solution of 1C was bleached
entirely upon irradiation with visible light (λ > 500 nm),
and its absorption spectrum returned to its initial state. In
the photostationary state, a clear isosbestic point was
observed at 309 nm, which supported the reversible two
2
4
compound was purified by column chromatography on
silica gel using the mixture solvent of petroleum ether
and ethyl acetate (v/v = 8/1) as the eluent to give the tar-
get compound 1O (0.20 g, 0.30 mmol) as a yellow solid in
6
0% yield. M.p. 343‐344 K; Anal. calcd for C H F N OS
34
23
6
3
2
[
54]
(
%): Calcd: C, 61.16; H, 3.47; N, 6.29. Found: C, 61.18; H,
1
3.46; N, 6.28; H NMR (DMSO, 400 MHz, TMS), δ (ppm):
2.03 (s, 6H), 4.58 (d, J = 8.0 Hz, 2H), 6.11 (d, J = 8.0 Hz,
1H), 7.05 (d, J = 12.0 Hz, 1H), 7.32 (t, J = 8.0 Hz, 1H),
7.39 (t, J = 6.0 Hz, 1H), 7.46 (d, J = 8.0 Hz, 1H), 7.49 (s,
1H), 7.51 (s, 2H), 7.54 (s, 1H), 7.63 (s, 1H), 7.66 (d,
(
A)
(B)
0
0
0
0
0
.4
.3
.2
.1
.0
0
4
8
12
16
20
Repeat cycles
(C)
FIGURE 1 Changes in the absorption and fluorescence spectra of 1O upon alternating irradiation with UV and visible light in acetonitrile
2.0 × 10‐5 mol/L): A, absorption spectral change; B, fluorescence change, excited at 400 nm; C, fatigue resistance
(

ZHANG ET AL.
5 of 11
[
55]
component photochromic reaction schemes.
The cycli-
Figure 2A. Results showed that the fluorescence and color
2+
zation and cycloreversion quantum yields of 1 were deter-
mined in acetonitrile by using 1,2‐bis(2‐methyl‐5‐phenyl‐
‐thienyl)perfluorocyclopentene as a reference (Figure
S10), and the values were measured as 0.78 and 0.14 (Fig-
ure S11). Figure 1B shows the fluorescence spectral change
of 1O upon photoirradiation in acetonitrile. The emission
peak of 1O was observed at 594 nm when excited at
of 1O changed significantly only when Cu was added to
its solution. Compared with that of 1O, 1O′ displayed a
remarkable blue shift from 594 to 524 nm (Figure 2A)
with a significant fluorescence color change from yellow
to bright green (Figure 2B). The result indicated that 1O
could be a highly selective fluorescent chemosensor for
3
2+
the recognition of Cu .
4
00 nm. Along with the photoisomerization, the emission
The excitation spectra of the complex 1O′ was mea-
sured in acetonitrile. The complex 1O′ shows a maximum
excitation peak centered at 400 nm when the emission is at
524 nm (Figure S12). The changes in the fluorescence of 1O
intensity at 594 nm decreased gradually. When the
photostationary state was reached, its emission intensity
decreased significantly by approximately 96%. The residual
fluorescence in the photostationary state may be attributed
to the incomplete cyclization reaction and the existence of
residual open‐ring isomers. Back irradiation of the appro-
priate wavelength of visible light (λ > 500 nm) regenerated
the open‐ring isomer 1O and recovered the original emis-
2+
induced by Cu /EDTA and light stimuli were investi-
−
5
gated in acetonitrile (2.0 × 10 mol/L) at room tempera-
ture, and the results are shown in Figure 3. Decline in
emission intensity at 524 nm was observed for 1O when
2+
the Cu concentration increased from 0 to 6.0 equiv,
followed by a plateau with further titration. The subse-
quent addition of an excess of EDTA did not recover its
original fluorescence intensity suggesting that the sensing
[53]
sion spectra. The fatigue resistance
of 1 was tested by
alternative irradiation with UV/vis light in air at room tem-
perature, as shown in Figure 1C. The coloration‐
decoloration cycles between 1O and 1C could be repeated
with only the degradation of 5% after 10 times and 7% after
2+
process of 1O in response to Cu was irreversible.
Meanwhile, in study on the fluorogenic quantitative
2+
2
0 times, which was detected by UV/vis spectral analysis,
sensing ability of Cu sensor, the binding ratio between
2+
respectively.
1O and Cu was calculated on the basis of the Job's plot
of the fluorescence intensity of 1O′ at 524 nm against the
molar fraction of 1O under the condition of an invariant
total concentration. The maximum value was achieved
3
.2 | Fluorescence response to metal ions
2
+
In this paper, the changes in the fluorescence of 1O
induced by metal ions, such as Cu , K , Ag , Ni ,
Co , Cd , Ba , Sn , Mg , Zn , Hg , Ca , Mn ,
Pb , Sr , Cr , Al , and Fe , were shown in
when the molar fraction of (1O)/[(1O) + (Cu )] was
0.5, indicating that the complex ratio of 1O′ is 1:1 in ace-
tonitrile (Figure 4A). The binding constant value of 1O
2+
+
+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
2+
3+
3+
3+
2+
with Cu was determined from the fluorescence titration
1
1
500
000
Blank and other ions
500
0
450 500 550 600 650 700 750
Wavelength (nm)
(A)
(B)
−
5
FIGURE 2 Changes in the fluorescence of 1O induced by various metal ions (6.0 equiv) in acetonitrile (2.0 × 10 mol/L), excited at
00 nm: A, emission spectral changes; B, photos of fluorescence changes in acetonitrile
4

6
of 11
ZHANG ET AL.
Furthermore, the mass spectrum of 1O in acetonitrile
2+
was recorded up the addition of Cu . As shown in Figure
2+
S13, when 6.0 equiv of Cu was added into the solution
of 1O, a new peak at 730.1 (m/z), corresponding to
2
+
+
[
1
1O + Cu − H] , appeared. This further proved that
2+
O directly interacted with Cu to form a 1:1 complex.
Further, to elucidate the coordination mode of 1O
2+ 1
with Cu , H NMR titration experiment was conducted
in CD CN‐d . As shown in Figure 5, a prominent change
3
3
of the ―NH proton (H ) and the azomethine proton (H )
a
b
was observed from the spectra of 1O before and after the
2+
treatment with different equivalent of Cu . Upon grad-
2+
ual addition of Cu , the ―NH proton (H ) signal disap-
a
peared ultimately, probably because of the influence of
FIGURE 3 Changes in fluorescence of 1O in acetonitrile
2+
−
5
2+
the Cu . Likewise, the azomethine proton (H ) signal
(
2.0 × 10 mol/L) induced by Cu /ethylene diamine tetraacetic
b
acid (EDTA), excited at 400 nm: emission intensity changes of 1O
changed from double peak to single peak, suggesting the
direct involvement of azomethine N atom in bonding to
2
+
induced by the addition of Cu
2+
2+
Cu . At the same time, with the addition of Cu , the sig-
nal of the phenyl protons (H , H , and H ) all experienced
profiles for the plots measured at 524 nm following the
c
d
e
[
32]
[56]
modified Benesi‐Hildebrand equation.
The association
an slight downfield shift. This observation was possibly
due to the coordination between Cu and the 2,1,3‐
2+
2+
constant (Ka) of 1O with Cu was calculated to be
.15 × 10 L/mol (Figure 4B). Additionally, the limit of
was measured to be
.84 × 10 mol/L (3δ per slope) (Figure 4C).
5
2
benzoxadiazole N atom of 1O. Therefore, the formation
2+
detection of 1O toward Cu
4
of the complex 1O′ was proposed as shown in Figure 5
‐
6
[2,18,57–59]
according to the reported method.
1
00
0
0
0
0
.48
.40
.32
.24
0
Y=B*X+A
A=0.1885
B=0.08758
R=0.9952
-
-
-
-
-
-
100
200
300
400
500
600
0.0
0.2
0.4
0.6
0.8
1.0
0.8
1.6
2.4
3.2
χ
= [1O]/([1O]+[Cu2+])
[Cu ] (Mol L) ×105
2+ -1
-1
(
A)
(B)
1
1
200
000
Y=B*X+A
A=314.2
B=27.7
R=0.99069
8
6
4
00
00
00
0
5
10
15
20
25
30
[
Cu2+](µM)
(C)
−
5
FIGURE 4 Job's plot, the limit of detection and Hildebrand‐Benesi plot for 1O in acetonitrile (2.0 × 10 mol/L): A, Job's plot showing the
2
+
2+
1
:1 complex of 1O and Cu ; B, Hildebrand‐Benesi plot based on the 1:1 for 1O, the binding constant of 1O with Cu was calculated to be
5
2+
−6
2
.15 × 10 L/mol; C, limit of detection for Cu is 4.84 × 10 mol/L

ZHANG ET AL.
7 of 11
2
+
FIGURE 5 1H nuclear magnetic resonance spectra (400 MHz) measured during the titration of 1O with Cu in CD3CN‐d
3
: (i) free 1O; (ii)
2
+
1
O + 6.0 equiv of Cu
The interferential experiments were performed to con-
Furthermore, the fluorescence of the complexes 1O′
showed photoswitchable properties upon alternating irra-
diation with UV/vis lights. Upon irradiation with 297‐nm
light, as the photocyclization reactions of 1O′ → 1C′ occur-
rence, both the fluorescence intensity decreased notably
because of the formation of weak fluorescent ring‐closed
isomers 1C′. Upon further irradiation to the
photostationary state, the fluorescence intensity of 1C′
was quenched to 52% (Figure 7A). Reversely, the ring‐
closed fluorescence intensity of 1C′ could return to the
original states when irradiated with appropriate visible
light.
2+
firm the selectivity for Cu (Figure 6A). Upon the induc-
2+
tion of Cu (6.0 equiv) in the presence of the same
+
+
2+
2+
concentration of other metal ions (K , Ag , Ni , Co ,
2+
2+
2+
2+
2+
2+
2+
2+
2+
Cd , Ba , Sn , Mg , Zn , Hg , Ca , Mn , Pb ,
Sr , Cr , Al , and Fe ), all the coexistent metal ions
solution (except for Cu ) displayed significant changes
with a remarkable blue shift from 594 to 524 nm. These
2
+
3+
3+
3+
2+
2
+
results demonstrated that the 1O could detect Cu selec-
tively and sensitively from other metal ions. Meanwhile,
competitive tests have been conducted for the fluores-
cence responses of 1O to various metal ions in acetoni-
trile. As shown in Figure 6B, the result exhibited a
significant fluorescence color change from yellow to
bright green.
Compound
1O′
could
also
undergo
photoisomerization upon alternating irradiation with
UV/vis light. Upon irradiation with 297‐nm UV lights,
1
1
1
1
600
400
200
000
1O+Metal ions
O+Cu +Metal ions
1
8
6
4
2
00
00
00
00
0
K
Ag Ni Co Cd Ba Sn
Zn Hg Ca
Pb Sr Cr Al Fe Cu
Mn
Blank
Mg
(A)
(B)
−
5
FIGURE 6 Changes in the fluorescence of 1O induced by various metal ions (6.0 equiv) in acetonitrile (2.0 × 10 mol/L), excited at
2+
4
00 nm: A, black bars represent the addition of 6.0 equiv of other metal ions to the solution of 1O. Red bars represent the addition of Cu
(
6.0 equiv) to the above solution; B, photos of competitive tests for the fluorescence responses of 1O to various metal ions in acetonitrile

8
of 11
ZHANG ET AL.
(
A)
(B)
−5
FIGURE 7 A, Changes in the fluorescence of 1O′ in acetonitrile (2.0 × 10 mol/L) upon alternating irradiation with UV and visible light;
−
5
B, changes in absorption spectra of 1O′ induced by photoirradiation in acetonitrile (2.0 × 10 mol/L)
(A)
(B)
2
+
FIGURE 8 A, Photochromism, color, and fluorescence changes of 1O induced by Cu and UV/vis; B, the combinational logic circuits
2
+
equivalent to the truth table given in Table 1: In1 (297‐nm light), In2 (>500‐nm light), In3 (Cu ), and output (fluorescence at 524 nm)

ZHANG ET AL.
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2
+
TABLE 1 All possible combinations of the input bit values and
their corresponding output values
to addition of Cu . The absorption intensity of
diarylethene 1O inceased by irradiation with 297‐nm UV
light, then diarylethene 1C decreased by addition of
Input
a
Output λ
2+
Cu . The emission intensity of diarylethene 1O at
24 nm was used as an initial state. The output signal could
2
+
ln1 (UV)
ln2 (Vis)
ln3 (Cu
)
em = 524 nm
5
0
1
0
0
1
1
0
1
0
0
1
0
1
0
1
1
0
0
0
1
0
1
1
1
0
0
0
1
0
0
1
1
serve as “on”, when the emission intensity at 524 nm was 3
times higher than the initial value. Otherwise, it was
regarded as “off”. All of the possible logic strings of the 3
inputs are listed in Table 1 and the logic circuit equivalent
to the truth table was shown in Figure 8B.
4
| CONCLUSIONS
a
In conclusion, a novel diarylethene linking a 2,1,3‐
At 524 nm, the emission intensity above the initial state is defined as 1; oth-
benzoxadiazole unit was designed and synthesized, and
erwise, defined as 0.
2
+
its photochromic behaviors with light and Cu were
investigated systematically. The results indicated that
the colorless solution of 1O′ turned light blue, a new
absorption band centered at 594 nm emerged because
of the formation of the closed‐ring isomer 1C′.
Reversely, the light‐blue solution turned colorless and
the absorption spectrum reverted to that of the original
open‐ring isomer 1O′ upon irradiation with visible light
2
+
the diarylethene was highly selective toward Cu in
acetonitrile. What is more, it has remarkable fatigue resis-
tance and excellent anti‐interference performance. On the
basis of the phenomenon, a logic circuit was constructed
by using the absorption intensity as the output signal with
2+
(Figure 7B). The cyclization and cycloreversion quantum
the inputs of Cu and UV/vis stimuli. Our experimental
results will be helpful for the design and construction of
new chemosensor with high selectivity and lower limit
of detection in the future.
yields of 1′ were determined in acetonitrile by using 1,2‐
bis(2‐methyl‐5‐phenyl‐3‐thienyl)perfluorocyclopentene
as a reference, and the values were measured as 0.73
and 0.12 (Figure S14).
ACKNOWLEDGEMENTS
3.3 | Application as a logic circuit
The authors are grateful for the financial support from the
National Natural Science Foundation of China (21662015),
the Science Funds of Natural Science Foundation of
Jiangxi Province (20171ACB20025, 20171BAB213018),
the “5511” Science and Technology Innovation Talent
Project of Jiangxi Province (20165BCB18015), the Science
Funds of Jiangxi Science & Technology Normal University
The interconversions among the different states of 1 were
described in Figure 8A. All these results demonstrated that
the fluorescence of diarylethene 1O could be effectively
2+
modulated by the stimulation with Cu and UV/vis lights
in acetonitrile. Furthermore, the mechanism of the absorp-
tion and emission intensity changes for 1O in the presence
2+
of Cu by photoirradiation was proposed as shown in
Figure 8A. Molecular logic is an interdisciplinary research
field, which has captured worldwide interest. As men-
tioned previously, the emission intensity of 1O could be
modulated by either light or chemical stimuli in acetoni-
trile (Figure 8A). On the basis of the fact that the emission
intensity of the target compound could be effectively
(
2016XJZD003), and the innovation fund of graduate
student (YC2016‐X03).
ORCID
Hongliang Liu http://orcid.org/0000-0001-5424-2978
2+
controlled by Cu and UV/vis stimuli, a logic circuit was
constructed by 3 inputs UV (297 nm, In1), vis (In2), and
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switched to “on” state with a Boolean value of “1”. In the
same way, In2 was “1” corresponding to the irradiation
with appropriate visible light, In3 was “1” corresponding
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