A highly selective fluorescent probe for detection of Cd2+ and HSO3- based on photochromic diarylethene with a triazole-bridged coumarin-quinoline group

Article abstract of DOI:10.1039/c8ra03443e

A novel photochromic diarylethene containing a quinoline-linked 3-aminocoumarin Schiff base unit (1O) was synthesized and used for the selective detection of Cd²⁺ and HSO₃^-. The synthesized probe exhibited a straightforward response for the selective detection of Cd²⁺. Its fluorescence emission red-shifted ～126 nm and was enhanced 24.9 fold in the presence of Cd²⁺. Meanwhile, the fluorescence color of 1O changed from dark cyan to golden yellow. The binding stoichiometry between 1O and Cd²⁺ was determined to be 1:1. A molecular logic circuit with three inputs and one output was successfully constructed with its light and metal-responsive behaviors. In addition, 1O was able to selectively recognize HSO₃^- with a 135-fold enhanced fluorescence emission and a notable fluorescence color change from dark cyan to bright cyan. The ¹H NMR and mass spectrometry analyses suggest that the HSO₃^- sensing of 1O is based on the hydrolysis of the Schiff base group of 1O.

Full text of DOI:10.1039/c8ra03443e

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PAPER
A highly selective fluorescent probe for detection
2
+
ꢀ
of Cd and HSO based on photochromic
3
Cite this: RSC Adv., 2018, 8, 22786
diarylethene with a triazole-bridged coumarin-
quinoline group
Shuli Guo, Gang Liu,* Congbin Fan
and Shouzhi Pu*
A novel photochromic diarylethene containing a quinoline-linked 3-aminocoumarin Schiff base unit (1O)
2+
3ꢀ
was synthesized and used for the selective detection of Cd
and HSO . The synthesized probe
2+
exhibited a straightforward response for the selective detection of Cd . Its fluorescence emission red-
2+
shifted ꢁ126 nm and was enhanced 24.9 fold in the presence of Cd . Meanwhile, the fluorescence
2+
color of 1O changed from dark cyan to golden yellow. The binding stoichiometry between 1O and Cd
was determined to be 1 : 1. A molecular logic circuit with three inputs and one output was successfully
Received 22nd April 2018
Accepted 8th June 2018
constructed with its light and metal-responsive behaviors. In addition, 1O was able to selectively
3ꢀ
recognize HSO with a 135-fold enhanced fluorescence emission and a notable fluorescence color
DOI: 10.1039/c8ra03443e
1
change from dark cyan to bright cyan. The H NMR and mass spectrometry analyses suggest that the
3ꢀ
rsc.li/rsc-advances
HSO sensing of 1O is based on the hydrolysis of the Schiff base group of 1O.
addition of bisulte to beer and wine has been customary for
1
. Introduction
centuries in most countries. However, it has been found that
ꢀ
Among various heavy metal ions, cadmium(II) is one of the most some individuals are sensitive to high concentrations of HSO
3
1,2
dangerous ions due to its high toxicity and carcinogenicity. As with the syndromes of asthmatic attack, gastrointestinal
2
+
17–22
we know, Cd has been widely used in many elds such as distress, allergic reaction and skin allergy.
Thus, the bisul-
3
,4
industry, agriculture, metallurgy, etc. However, high levels of te content in foodstuffs has been strictly limited in many
Cd can impose huge threats to the environment and human countries. For this reason, the selective and sensitive chemo-
2
+
5,6
health due to its bioaccumulation through the food chain.
sensors of bisulte are highly desired. To date, many of the
2
+
ꢀ
Excessive intake of Cd can not only increase the risk of cancer, reported HSO
3
sensors have based on different reaction
7–10
23,24
heart disease, cardiovascular diseases and diabetes,
damage the liver and kidneys. As a highly toxic heavy metal, complexation with amines,
cadmium has been listed on the “CERCLA Priority List of reaction with aldehyde or levulinate.
Hazardous Substances” of Toxic Substances and Disease et al. Reported a mitochondria-targeted probe derived from the
but also mechanisms, including coordination to metal ions,
25,26 27–32
Michael additions,
selective
33–35
For instance, Zeng
11
Registry (ATSDR). Thus, efficient methodologies for selective conjugation of carbazole and benzo[e]indolium, to which 1,4-
36
2
+
detection of Cd are desperately needed. One of the greatest nucleophilic addition reaction with bisulte occurred.
2
+
3ꢀ
challenges in Cd detection is the highly similar binding However, there are no reports for HSO sensors, which based
2
+
2+
properties of Cd and Zn that are located in the same group on Schiff base with hydrolysis mechanisms.
12
of the periodic table. Therefore, the development of highly
A variety of advanced technologies, such as inductively
2
+
2+
37
selective sensors of Cd without interferences from Zn under coupled plasma-atomic emission spectrometry (ICP-AES),
38
physiological conditions has become a hot research topic.
atomic absorption spectroscopy (AAS) and inductively coupled
Anions play important roles in biological, medical, envi- plasma-mass spectrometry (ICP-MS), have been widely used
39
2
+
ꢀ
3
1
3–15
ronmental and chemical sciences.
bisulte (HSO
Among various anions, for the analysis of Cd and HSO . By comparison, uorescent
ꢀ
) is one of the most concerned anions, which probes are superior and have attracted increasing attentions in
3
has been widely used as an enzyme inhibitor, antimicrobial ion detections in both chemistry and biology due to their high
16
40–46
agent, beverages, and an antioxidant for foods. In fact, sensitivity, good selectivity, easy operation, and low cost.
Among the reported photo-responsive materials, diary-
lethene is one of the most promising photo-switchable mole-
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal cules, which have exhibited great potentials in optical
University, Nanchang 330013, PR China. E-mail: pushouzhi@tsinghua.org.cn; Fax:
information storage media and photonic switch devices with
+
86 791 83805870; Tel: +86 791 83805870; +86 791 83831996
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Scheme 1 Photochromism of diarylethene 1O.
2
+
3ꢀ
their excellent photo reactivity, thermal stability, and fatigue uorescent responses to Cd and HSO were systematically
resistance.
47–51
Moreover, diarylethenes have also been exten- discussed. Scheme 1 shows the photochromic process of 1O.
sively introduced to application in electronic logic devices in
recent years, because they exhibit excellent optical perfor-
mances and multi-response to various ions owing to their
2
. Experiments
52–54
special structures.
As known to all, electronic equipment 2.1 General methods
has gradually become a necessity in people's lives and the logic
circuits are essential for the fabrication of optoelectronic
devices. According to the above advantages, an increasing
number of diarylethenes were introduced to uorescent sensor
for detection of different ions in recent years. For instance, Li
All solvents were of analytical grade and distilled before use.
Other reagents were used as-received. H NMR and C NMR
spectra were recorded on a Bruker AV400 spectrometer (400
1
13
3 3
MHz) using DMSO-d6, CDCl and CD CN as the solvents and
tetramethylsilane (TMS) as the internal standard. Mass spectra
were obtained using an Agilent 1100 Ion Trap LC/MS MSD
system. Infrared spectra (IR) were collected on a BrukerVertex-70
spectrometer. Melting points were measured using a WRS-1B
2
+
et al. reported a highly selective uorescent probe for Cd and
2
+
Zn based on a new diarylethene with quinoline–benzimid-
55
azole conjugated system, Zhang et al. reported a uorescent
2
+
sensor for Cd based on a new diarylethene with a 1,8-naph-
2+
+
melting point apparatus. All metal ions, except for Hg and K
5
6
2+
thyridine unit, Duan et al. studied a uorescent probe for Cd
based on diarylethene with pyridinepiperazine-linked
that were prepared with their chloride salts, were obtained by
dissolving the corresponding metal nitrates (0.1 mmol) in
distilled water (10 mL). All anions were obtained by dissolving
the corresponding potassium or sodium salts (0.1 mmol) in
distilled water (10 mL). The EDTA solution was prepared with
a
57
hydroxyquinoline group. However, there are no diarylethene-
based chemosensors that exhibit uorescence response to
2
+
ꢀ
both Cd and HSO . Thus, development of uorescent probes
3
2
+
ꢀ
toward Cd and HSO3 are still challenging.
2
ethylenediaminetetraacetic acid disodium salt (Na EDTA) (1.0
In this study, we designed and synthesized a novel photo-
chromic diarylethene bearing a quinoline-linked 3-amino-
coumarin Schiff base unit (1O), and its photochromic and
mmol) in distilled water (10 mL). Fluorescence spectra were
measured with a Hitachi F-4600 uorescence spectrophotom-
eter. UV-vis absorption spectra were recorded on an Agilent 8453
Scheme 2 Synthetic routes of diarylethene 1O.
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UV/vis spectrophotometer equipped with an MUA-165 UV lamp quantum yield spectrometer. Photoirradiation was conducted
and MVL-210 visible lamp for photoirradiation. Fluorescence on a setup consisting of an SHG-200 UV lamp, Cx-21 ultraviolet
quantum yield was measured using a QY C11347-11 absolute PL uorescence analysis cabinet, and BMH-250 visible lamp.
ꢀ5
ꢀ1
Fig. 1 (A) Changes in the absorption spectrum of 1O in acetonitrile (2.0 ꢂ 10 mol L ) upon alternating irradiation with UV and visible light; (B)
fatigue resistance of 1O in acetonitrile under the alternating irradiation at room temperature.
ꢀ
5
ꢀ1
2+
Fig. 2 Changes in the absorption spectrum and color of 1O in acetonitrile (2.0 ꢂ 10 mol L ) in response to Cd /EDTA and light stimuli. (A)
2+
2+
Spectral changes of 1O induced by Cd /EDTA; (B) spectral changes of 1O + Cd induced by UV/vis light; (C) spectral changes of 1C induced by
2+
Cd /EDTA.
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2
1
.2 Synthesis of 1O
to room temperature and ltered. The residue was washed with
cold methanol to afford 1O (0.22 g) in 81% yield. Mp: 439–440 K;
O was synthesized following the route shown in Scheme 2.
1
H NMR (400 MHz, DMSO, ppm): d 2.35 (s, 3H, –CH ), 3.00 (s,
3
Compounds 2 and 3 were prepared by the methods reported in
58,59
3H, –CH
H, –CH]N–), 7.15 (s, 1H, Ar–H), 7.29 (d, 1H, Ar–H), 7.35 (t, 3H,
Ar–H), 7.40 (s, 1H, Ar–H), 7.42 (s, 2H, Ar–H), 7.47 (q, 2H, Ar–H),
3 2 2
), 5.45 (s, 2H, –CH –N–), 5.72 (s, 2H, –CH –O–), 6.18 (d,
literature.
.2.1 Synthesis of compound 4. The NaVc (0.04 g, 0.20
mmol) and CuSO (0.025 g, 0.10 mmol) solution in water (10
mL) was added to a solution of 2 (0.55 g, 1.00 mmol) and 3
0.21 g, 1.00 mmol) in THF (40 mL) under stirring at room
1
2
4
7
1
.52 (s, 1H, Ar–H), 7.54 (s, 1H, Ar–H), 7.60 (q, 2H, Ar–H), 7.62 (s,
H, Ar–H), 7.79 (d, 1H, Ar–H), 7.94 (d, 1H, Ar–H), 8.51 (d, 2H, Ar–
(
1
3
H); C NMR (100 MHz, DMSO, TMS): d ¼ 14.56, 15.07, 50.17,
temperature. The reaction mixture was stirred at room
temperature for 12 h to allow the Cu(I)-catalyzed 1,3-dipolar
cycloaddition reaction of 2 and 3, and extracted with CH
5
1
1
1
1
1
C
3.01, 63.50, 83.50, 109.65, 111.73, 116.18, 119.37, 120.60,
20.75, 121.62, 121.92, 123.07, 123.36, 124.59, 124.86, 125.29,
25.71, 125.99, 126.36, 127.07, 127.98, 129.35, 130.98, 132.67,
36.35, 137.81, 138.11, 138.42, 141.20, 142.07, 143.62, 144.23,
2 2
Cl .
The organic phase was dried over Na SO , ltered and evapo-
2
4
rated. The crude product was puried by silica gel column
chromatography using petroleum dichloro/ethyl acetate (v/v ¼
ꢀ
1
48.55, 154.11, 154.52, 159.14; IR (KBr, v, cm ): 1715 (–C]O),
628 (–C]N), 1338 (–C–N), 1275 (–C–O); MS (m/z): Calculated for
1/1) as the eluent to afford 0.51 g compound 4 as a purple solid
+
+
1
H F N O S
48 31 6 5 3 2
[M] : 903.1773, found: 904.1836 for [1O + H]
in 67% yield. H NMR (400 MHz, CDCl , ppm): d 1.94 (s, 3H,
3
+
and 926.1658 for [1O + Na] .
–
–
CH ), 2.29 (s, 3H, –CH ), 5.30 (s, 1H, –CH –N–), 5.52 (s, 2H,
3 3 2
CH –O–), 5.59 (s, 2H, Ar–H), 7.16 (s, 1H, Ar–H), 7.23 (s, 1H, Ar–
2
H), 7.25 (s, 1H, Ar–H), 7.33 (q, 2H, Ar–H), 7.41 (q, 3H, Ar–H), 7.50
3
. Results and discussion
(
d, 1H, Ar–H), 7.59 (m, 2H, Ar–H), 7.73 (t, 1H, Ar–H), 8.06 (d, 1H,
Ar–H), 8.28 (d, 1H, Ar–H), 10.26 (s, 1H, –CHO).
.2.2 Synthesis of (1O). Compound 4 (0.23 g, 0.3 mmol) was The photochromic behavior of diarylethene 1O induced by UV/
reuxed with 3-aminocoumarin (0.048 g, 0.3 mmol) in anhy- vis light was investigated in acetonitrile (C
2.0
drous methanol (5.0 mL) at 80 C under stirring for 1 h, cooled 10 mol L ) at room temperature. As shown in Fig. 1A, the 1O
3.1 Photochromic of diarylethene 1O
2
¼
ꢂ
ꢃ
ꢀ5
ꢀ1
ꢀ5
ꢀ1
Fig. 3 Fluorescence changes of 1O (2.0 ꢂ 10 mol L ) in acetonitrile in response to various metal ions (2.4 equiv.). (A) Fluorescence emission
2+
spectra of 1O in the presence of various metal ions; (B) fluorescence emission spectra of 1O in the presence of Cd ; (C) image demonstrating
the solution color of 1O in the presence of different metal ions.
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solution in acetonitrile is colorless, exhibiting a sharp absorp- change from colorless to yellow, due to the formation of
2
+
tion peak at 242 nm due to the p–p* transition. A new complex 1O + Cd . The addition of an excess amount of EDTA
2
+
absorption band centered at 547 nm appeared upon the irra- did not restore the original color of 1O, suggesting that the Cd
diation with 297 nm light, accompanied with a visible color sensing process of 1O was irreversible (Fig. 2A). As depicted in
2
+
change from colorless to purple, due to the photocyclization of Fig. 2B, the 1O + Cd complex was also photoisomerized under
60–62
1O to 1C.
The photocyclization reaction reached the pho- the alternating irradiation with UV and visible light. Upon the
tostationary state (PSS) in 4.5 min under the irradiation of UV irradiation with 297 nm UV light, the yellow solution of 1O +
2
+
light, where a clear isosbestic point was observed at 300 nm. Cd turned plum and a new absorption band emerged at
3
ꢀ1
ꢀ1
These observations suggest that the irritation caused a two- 547 nm (3max ¼ 8.5 ꢂ 10 mol L cm ) due to the formation of
63ꢀ65
2+ 66,67
component photochromic reaction.
The absorption spec- the closed-ring isomer 1C + Cd .
Reversely, the plum solu-
trum was successfully restored to the original state, accompa- tion turned yellow, and the absorption spectrum was restored to
2
+
nied by the color change from purple to colorless, by irradiating that of the open-ring isomer 1O + Cd upon irradiation with
2
+
the 1C solution with visible light. The cyclization and cyclo- visible light. Directly adding Cd to the solution of 1C weak-
reversion quantum yields were calculated to be 0.139 and 0.324, ened the absorption band centered at 322 nm and enhanced the
respectively. The fatigue resistance of 1O was tested by alter- absorption at 393 nm. Meanwhile, the solution color changed
2
+
nating irradiation with UV and visible light at room tempera- from purple to plum, indicating that 1C and Cd formed 1C +
2
+
ture. Ten coloration–decoloration cycles of 1O caused only 6.5% Cd complex. It is worth noting that the complexation between
2
+
degradation (Fig. 1B).
1C and Cd was not be reversed by EDTA either (Fig. 2C). These
2
+
results indicate that both isomers of 1O have stronger Cd
2
+
binding ability than EDTA.
3.2 Changes in absorption spectrum induced by Cd
Fig. 2 shows the absorption spectra and colors of 1O induced by
2
+
3.3 Fluorescence response of 1O to metal ions
Cd /EDTA and UV/vis stimuli in acetonitrile. A new absorption
2
+
ꢀ5
ꢀ1
band appeared at 392 nm as Cd added and the band intensity The uorescence and color responses of 1O (2.0 ꢂ 10 mol L
2
+
increased with the increase of Cd amount and reached the in acetonitrile) to various metal cations (2.4 equiv.) including
2
+
2+
3+
3+
3+
2+
2+
2+
2+
2+
2+
+
maximum at 1.8 equiv. of Cd , accompanied by a notable color Cd , Cr , Al , Fe , Cu , Zn , Co , Mn , Hg , Pb , K ,
ꢀ
5
ꢀ1
2+
Fig. 4 (A) Competitive tests for the fluorescence response of 1O (2.0 ꢂ 10 mol L ) in the presence of Cd and other competing metal ions in
acetonitrile. Black bars represent the fluorescence intensities of 1O in the presence of 2.4 equiv. metal ions. Red bars represent fluorescence
2+
intensity of 1O at 633 nm as in the presence of Cd (2.4 equiv.) and other competing metal ions. (B) Emission spectra of 1O solutions containing
Cd (2.4 equiv.) and the competing metal ions; (C) fluorescence color of 1O in the presence of Cd and other competing metal ions.
2+
2+
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ꢀ
5
ꢀ1
2+
Fig. 5 Fluorescence responses of 1O (2.0 ꢂ 10 mol L ) to Cd /EDTA in acetonitrile, excited at 392 nm. (A) Fluorescent emission spectra of
2+
2+
1
O titrated with different amounts of Cd ; (B) fluorescence intensities of 1O at 633 nm as titrated with different equiv. of Cd ; (C) fluorescent
emission spectra of 1O + Cd under alternating photoirradiation with UV and visible light; (D) Job's plot showing the 1 : 1 complex of 1O with
2+
2+
Cd
.
2
+
2+
2+
2+
+
2+
Ca , Mg , Ba , Sr , Ag and Ni were investigated with emission at 507 nm of 1O (Fig. 3A). The uorescence emission
3
+
3+
3+
3+
3+
a uorescence spectroscopy. All metal ions except for Cr , Al
and Fe caused no obvious changes in the uorescence added, companied by the color change from dark cyan to bright
of 1O at 507 nm was dramatically enhanced as Cr , Al or Fe
3
+
2+
Fig. 6 ESI-MS spectra of 1O in the absence of presence of Cd in acetonitrile.
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cyan (Fig. 3C). However, the maximum emission peak had an cations listed above. As shown in Fig. 4, the uorescence
2
+
obvious red-shi from 507 nm to 633 nm upon the addition of response of 1O to Cd was not signicantly affected by other
2
+
2+
Cd to 1O in acetonitrile, we can see this phenomenon more competing metal ions, except for Cu that caused a reduction
2
+
clearly through Fig. 3B. The structural rigidity of the Cd
complexes and metal binding close to the diarylethene might be emission intensity and uorescence color induced by Cd
the factors that cooperate to induce the large emission peak alone, the interference of Cu is negligible. As mentioned
shi. Meanwhile, it's emission intensity enhanced by 24.9 folds above, most Cd uorescent probes encounter the interference
with the stimulation of 2.4 equiv. of Cd , accompanied by from Zn that is located in the same group in the periodic table
a color change from dark cyan to golden yellow. These results and has similar chemical properties to Cd . Yet such interfer-
indicate that 1O can selectively recognize Cd over other metal ence was not observed in the Cd chemosensing of 1O too.
ions in acetonitrile.
in emission intensity. However, compared with the variations of
2
+
2
+
2
+
2
+
2+
2
+
2
+
2+
2
+
These results suggested that 1O is highly selective to Cd over
2
+
3+
3+
3+
2+
To further demonstrate the selectivity of 1O towards Cd in other competing cations, even Cr , Al , Fe , and Zn in
acetonitrile, competitive experiments were conducted on Cd
in the presence of equal equivalent of other competitive metal
2
+
acetonitrile.
2+
Fig. 7 (A) Changes in the photochromism, color, and fluorescent of 1O induced by Cd /EDTA and UV/vis lights; (B) the combinational logic
2+
circuit equivalents to the truth table in Table 1, where In1 (297 nm UV light), In2 (500 nm visible light), In3 (Cd ) are inputs, and O1 is output.
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Table 1 Truth table for all possible strings of three binary-inputs and by a plateau with further titration (Fig. 5B). Meanwhile, the
a
the corresponding output digits

uorescence color changed from dark cyan to golden yellow.
2
+
The uorescence quantum yield of 1O + Cd was determined to
Input
be 0.031, 14.5-fold greater than that of 1O (F , 1O ¼ 0.002). The
f
2
+
In1 (UV)
In2 (Vis)
In3 (Cd
)
Output lab ¼ 393 nm 126 nm re-shi of emission peak and up to 24.9-fold enhanced
emission intensity suggest that 1O is an ideal uorescent che-
0
0
1
0
1
0
1
1
0
0
0
1
0
1
1
1
0
1
0
0
1
1
0
1
0
1
0
0
0
1
0
1
2+
mosensor of Cd . The subsequent addition of excess EDTA did
not restore the uorescence to the original state of 1O, sug-
2
+
gesting that the Cd sensing process of 1O was irreversible. The
2
+
1O + Cd complex also exhibited photoswitchable uorescence
behaviors upon alternating irradiation with UV and visible
2+
light. The uorescence of 1O + Cd was quenched dramatically
with a clear color change from golden yellow to fawn brown
upon the irradiation with 297 nm light, due to the formation of
a
The output is dened as 1 if the absorbance at 393 nm is greater than
.18, otherwise it is dened as 0.
0
2
+
weak uorescence closed-ring isomer of 1C + Cd (Fig. 5C).
2
+
However, the uorescence intensity of 1O + Cd was only
reduced to ca. 34% at the photostationary state, possibly owing
to the incomplete cyclization and the formation of isomers with
parallel conformations. The back irradiation with appropriate
2
+
The uorescence responses of 1O to Cd /EDTA and light
stimuli were investigated in acetonitrile at room temperature.
The emission peak of 1O at 507 nm disappeared and a new peak
centered at 633 nm appeared as Cd added due to the forma-
2
+
visible light regenerated the open-ring isomer 1O + Cd and the
original emission intensity was recovered.
2
+
2
+
tion of 1O + Cd complex (Fig. 5A). The emission intensity at
Additionally, in order to determine the binding stoichiom-
2
+
2
+
633 nm linearly increased with the increase of Cd concen-
etry between 1O and Cd , the Job's plot with emission intensity
at 633 nm as a function of molar fraction of 1O was drawn. The
2
+
tration and reached the maximum at 2.4 equiv. Cd , followed
Fig. 8 Fluorescence responses of 1O (2.0 ꢂ 10ꢀ mol L in acetonitrile) to various anions (4.3 equiv.). (A) Fluorescence emission spectra of 1O in
5
ꢀ1
ꢀ
the presence of various anions; (B) competitive experiments for the fluorescence response of 1O to HSO
3
and other competing anions in
acetonitrile. Black bars represent fluorescence intensities of 1O in the presence of 4.3 equiv. competing anions. Red bars represent the fluo-
ꢀ
rescence intensities of the corresponding solutions after 4.3 equiv. HSO
3
added. More details can be found in the web version of this article; (C)
fluorescent color of the 1O solution in the presence of different anions.
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2
+
concentration of 1O + Cd reached the maximum at the molar Boolean value of ‘1’ or ‘0’. For example, In1 is ‘on’ with the
2
+
2+
fraction of [Cd ]/([Cd ] + [1O]) ¼ ꢁ0.5 (Fig. 5D), indicating that Boolean value of ‘1’ when 297 nm light is used. Similarly, In2 is
the binding stoichiometry was 1 : 1. The 1 : 1 coordination ‘1’ as irradiation with appropriate visible light (l > 500 nm) is
2
+
2+
stoichiometry of 1O with Cd was further conrmed by the ESI used and In3 is ‘1’ as Cd is added. The output is considered at
mass spectrometry (ESI-MS) analysis. 1O exhibited a character- ‘on’ state with the Boolean value of ‘1’ if the absorbance at
+
istic peak at 926.1658 m/z for [1O + Na] (calcd 926.1659) and 393 nm is greater 0.18. Otherwise, it is regarded at ‘off state with
04.1836 m/z for [1O + H] (calcd 904.1852), which disappeared the Boolean value of ‘0’. Table 1 lists all possible strings of the
as 2.4 equiv. of Cd were added, accompanied by the appear- binary inputs and the corresponding output digits. Upon the
ance of a new peak at 1016.0887 m/z for [1O + Cd ꢀ H] (calcd stimulation of different inputs, the diarylethene can exhibit an
+
9
2
+
2
+
+
1016.0884) (Fig. 6).
on–off–on photochromic switching behavior.
3.4 Application in logic circuits
3.5 Fluorescence response of 1O to anions
Based on the photochromic behaviors of the diarylethene 1O in The uorescence responses of 1O to a variety of anions
2
+
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2ꢀ
3ꢀ
response to Cd and UV/vis lights, a logic circuit was con- including HSO
3
, HSO
4
, F , Cl , Br , I , H
2
PO
4
, CO
3
,
,
2
+
2ꢀ
2ꢀ
ꢀ
2ꢀ
2ꢀ
3ꢀ
4ꢀ
structed with light irradiations and Cd as the inputs and the HPO
absorbance of 1O at 393 nm as the output (Fig. 7). As shown in NO
4
ꢀ
, SO
3
, SCN , SO
4
, S
2
O
3
, PO
4
, ClO , HCO
ꢀ
ꢀ
3
, Ac and CN were measured in acetonitrile to explore its
Fig. 7A, the absorption of 1O (output) can be effectively modu- potential application as a selective anion sensor. As shown in
lated by a logic circuit constructed with the three inputs Fig. 8A and C for the uorescence spectra of 1O in the presence
ꢀ
including In1: 297 nm UV light, In2: l > 500 nm visible light, and of 4.3 equiv. anions, none of them, except for HSO3 caused
2
+
In3: Cd (Fig. 7B). The output can be either ‘on’ or ‘off ’ with the notably uorescent emission at 510 nm and a uorescent color
ꢀ
5
ꢀ1
3ꢀ
Fig. 9 Changes in the fluorescence of 1O (2.0 ꢂ 10 mol L in acetonitrile) induced by HSO /EDTA and light stimuli at room temperature.
ꢀ
Excitation: 370 nm. (A) Fluorescence emission spectra of 1O titrated with different amounts of HSO
3
; (B) the fluorescence intensities of 1O at
ꢀ
ꢀ
5
10 nm in the presence of different equiv. HSO
3
; (C) fluorescence emission spectra of 1O + HSO
3
under the irradiation with UV and visible
lights.
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change from dark cyan to bright cyan. Compared with that of titration was conducted at room temperature. As shown in
O, the uorescence intensity was enhanced by 135.5 folds, Fig. 9A and B, the uorescence emission of 1O at 510 nm line-
1
ꢀ
ꢀ
suggesting that 1O can recognize HSO3 . The selectivity of the arly increased with the increase of HSO3 amount, accompa-
reorganization was further conrmed by competitive experi- nied by a notable uorescent color change from dark cyan to
ꢀ
ments. As depicted in Fig. 8B, all competing anions, except for bright cyan, and reached the maximum at 4.3 equiv. HSO
3
,
ꢀ
ꢀ
ꢀ
CN showed no obvious interference with the HSO
3
sensing.
followed by a plateau as HSO further added. The addition of
3
To further illuminate the responsive uorescent emission of excess EDTA did not recover its original uorescence intensity,
ꢀ
ꢀ
1O induced by HSO
3
and UV/vis irradiation, uorescence indicating that the HSO
3
sensing process of 1O was
1
3ꢀ
Fig. 10 (A) Partial H NMR spectra of 1O in the absence (a) and presence of 4.3 eq. (b) of HSO in deuterated acetonitrile; (B) ESI-MS spectrum of
ꢀ
1
O + HSO
3
.
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3ꢀ
Scheme 3 Possible hydrolysis reaction of 1O in the presence of HSO in acetonitrile.
irreversible (Fig. 9A). The absolute uorescence quantum yield shied emission peak and up to 24.9-fold enhanced uores-
ꢀ
of 1O + HSO3 was determined to be 0.048, 23 folds high than cence intensity, accompanied by a notable uorescent color
that of 1O (F
f
, 1O ¼ 0.002). These results suggest that the dia- change from dark cyan to golden yellow. The competitive
rylethene can also be potentially used as a uorescent probe for experiments suggest that such selective uorescent response of
the quantitative detection of HSO
also exhibited photoswitchable uorescence behavior upon including Zn . The binding stoichiometry between 1O and
alternating irradiation with UV and visible light. The uores- Cd was determined to be 1 : 1. Similarly, it was found that
ꢀ
ꢀ
2+
3
. The 1O + HSO
3
complex 1O to Cd is not interfered by other competing metal cations
2
+
2
+
ꢀ
ꢀ
cence of 1O + HSO3 was quenched dramatically with a clear HSO3 was able to enhance the uorescence emission of 1O in
color change from bright cyan to light cyan under the irradia- acetonitrile up to 135.5-fold and caused a notable uorescence
tion of 297 nm light, due to the formation of closed-ring isomer color change from dark cyan to bright cyan due to the hydrolysis
ꢀ
ꢀ
1C + HSO
3
(Fig. 9C). The uorescence intensity of 1O + HSO
3
of the C]N bond in 1O that produced an aldehyde and amine.
was weakened to ca. 32% at PSS due to the incomplete cycliza- These results suggest that the diarylethene derivative has a great
2
+
tion and existence of isomers with parallel conformations. application potential as a uorescent sensor of both Cd and
ꢀ
Upon the irradiation of visible light, the uorescent spectrum HSO
3
.
ꢀ
was restored to the initial state of 1O + HSO
3
.
ꢀ
To further explore the interaction between 1O and HSO in
3
1
Conflicts of interest
solution and determine the sensing mechanism, the H NMR
ꢀ
titration of 1O with HSO3 was performed in deuterated
There are no conicts of interest to declare.
acetonitrile. 1O exhibited a singlet at d 6.18 ppm of the imine
ꢀ
protons (N]CH) (Fig. 10A). As 4.3 equiv. HSO
3
was added to
the 1O solution, the singlet at d 6.18 ppm disappeared and
a new singlet appeared at d 10.26 ppm that was attributed to
aldehyde protons (–CHO). These results suggest that 1O was
Acknowledgements
The authors are grateful for the nancial support from the
National Natural Science Foundation of China (21363009,
ꢀ
hydrolyzed to afford compound 4 in the presence of HSO3 in
2
1662015), the “5511” science and technology innovation talent
acetonitrile, similar phenomena were also found in other re-
68–70
project of Jiangxi, the key project of Natural Science Foundation
of Jiangxi Province (20171ACB20025), the Science Funds
of Natural Science Foundation of Jiangxi Province
ported probes.
3ꢀ
The mass spectra of 1O and 1O + HSO more directly evi-
denced the reaction. As depicted in Fig. 10B, the peaks of 1O at
+
(20171BAB203014, 20171BAB203011).
9
26.1658 m/z for [1O + Na] (calcd 926.1659) and 904.1836 m/z
+
for [1O + H] (calcd 904.1852) disappeared aer 4.3 equiv.
ꢀ
HSO
3
added, and two new peaks appeared at m/z ¼ 759.1340
ꢀ
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3
9
26 6 4 2 2
ꢀ
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7
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1
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