A novel chromone derivative as dual probe for selective sensing of Al(III) by fluorescent and Cu(II) by colorimetric methods in aqueous solution

Article abstract of DOI:10.1016/j.jphotochem.2019.111955

Based on the chromone skeleton, a simple and novel probe that is 6-ethoxychromone-3-carbaldehyde-(furanyl) hydrazone (L) has been synthesized and completely characterized. It exhibited representative turn-on fluorescent properties and obviously colorimetric changes with high selectivity to Al³⁺ and Cu²⁺. For Al³⁺, L displayed a turn on green fluorescence in EtOH/H₂O (3/2) aqueous media over other common cations. With Cu²⁺, L perceived Cu²⁺ through the naked-eye by the color changed-from colorless to yellow. Moreover, the coordination ratio between L-Al³⁺and L-Cu²⁺ was 1:1 which could be verified by the Job's plot, ¹H NMR and high-resolution mass spectrum. Consequentially, L could be used as a solid probe for both Al³⁺ and Cu²⁺.

Full text of DOI:10.1016/j.jphotochem.2019.111955

Accepted Manuscript
Title: A novel chromone derivative as dual probe for selective
sensing of Al(III) by fluorescent and Cu(II) by colorimetric
methods in aqueous solution
Authors: Limei Tian, Jia Xue, Si-liang Li, Zheng-yin Yang
PII:
S1010-6030(19)30654-9
DOI:
Article Number:
https://doi.org/10.1016/j.jphotochem.2019.111955
111955
Reference:
JPC 111955
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
18 April 2019
21 June 2019
30 June 2019
Please cite this article as: Tian L, Xue J, Li S-liang, Yang Z-yin, A
novel chromone derivative as dual probe for selective sensing of Al(III)
by fluorescent and Cu(II) by colorimetric methods in aqueous solution,
Journal of Photochemistry and amp; Photobiology, A: Chemistry (2019),
https://doi.org/10.1016/j.jphotochem.2019.111955
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A novel chromone derivative as dual probe for selective
sensing of Al(Ⅲ) by fluorescent and Cu(Ⅱ) by colorimetric
methods in aqueous solution
a
a
b
a*
Limei Tian , Jia Xue , Si-liang Li , Zheng-yin Yang
aCollege of Chemistry and Chemical Engineering, State Key Laboratory of Applied
Organic Chemistry, Lanzhou University, Lanzhou 730000, PR China
bSchool of Petrochemical Engineering, Lanzhou University of Technology, Lanzhou
7
30050, PR China
*Corresponding author. Tel: +86 931 8913515; Fax: +86 931 812582; e-mail:
yangzy@lzu.edu.cn (Z.Y. Yang)
Graphical abstract
1

Highlights

A novel probe L for the detection of Al(Ⅲ) and Cu(Ⅱ) based on two different
mechanisms was synthesized.

L displayed a high selectivity and remarkable fluorescence enhancement for Al3+
2+
and perceived Cu through the naked-eye by the color changed-from colorless to
yellow.
3+
−7

The detection limit of L for sensing Al was calculated to be 1.801 × 10 M and
2+
−7
for Cu was 2.857 × 10 M.
This probe L demonstrated an excellent fluorescence sensing performance even

3+
2+
in the solid state for both Al and Cu .
2

Abstract
Based on the chromone skeleton, a simple and novel probe that is
6
-ethoxychromone-3-carbaldehyde-(furanyl) hydrazone (L) has been synthesized and
completely characterized. It exhibited representative turn-on fluorescent properties
3
+
2+
3+
and obviously colorimetric changes with high selectivity to Al and Cu . For Al , L
displayed a turn on green fluorescence in EtOH/H O (3/2) aqueous media over other
2
2
+
2+
common cations. With Cu , L perceived Cu through the naked-eye by the color
changed-from colorless to yellow. Moreover, the coordination ratio between
3
+
2+
1
L-Al and L-Cu was 1:1 which could be verified by the Job’s plot, H NMR and
high-resolution mass spectrum. Consequentially, L could be used as a solid probe for
3
+
2+
both Al and Cu .
2
+
3+
KEYWORDS: Fluorescent probe; Chromone derivative; Cu ; Al ; Colorimetric
probe.
Introduction
Recently, the design and development of probes with selective recognition and
2
+
3+
effective detection the Cu and Al ions have got a lot of attention [1, 2]. Especially
the probes can be used in biological processes [3]. Among these probes, the probes
based on colorimetric [4, 5] and fluorescence [6] have the advantages such as low cost,
excellent selectivity, simple operation, fast response and easy instrument
implementation [7, 8]. The fluorescent probes have been considered as one of the
most efficient methods in biological systems owing to their easiness of manipulating,
real-time imaging and nondestructive detection [9-11]. Up to now, keen interest is
2
+
3+
absorbed in expanding high selectivity and sensitivity probes for Cu and Al ions
by turn-on fluorescence and simple absorbance responses. The reason is that
aluminum is the third most substantial element in rock-soils and the most abundant
metallic elements (about 8% by weight) in the earth’s crust [12]. Aluminum has been
widely used in food packaging, metallurgy, conductive material and other fields
3

[13-15]. However, excessive aluminum has some negative effects on human's lives.
3
+
Aluminum ions (Al ) accumulate in the human body by the food chains and
3
+
eventually concentrate in the organism. Excessive accumulation of Al in the human
body is implicated as a causative factor of Alzheimer's disease and Parkinson's disease
2
+
[
16-18]. Simultaneously, the other essential element Cu exists in many enzymes. It
is a pivotal ion for energy production in physiological activities and participates in
electron transfer, superoxide dismutation, oxygen metabolism, nerve conduction
2
+
[
19-21]. Nevertheless, Cu can trigger disorders associated with neurodegenerative
diseases at relatively high levels [22-24]. Therefore, it becomes imperative to develop
3
+
2+
2+
3+
selective sensors of Al , Cu and distinguish between Cu and Al , synchronously,
with high selectivity and sensitivity. In consideration of the preeminent photophysical
properties sounds like less toxicity, high quantum yield and large absorption
coefficient, Chromone skeleton is an ideal model for constructing fluorescent probes.
Moreover, several cases of chromone-based probes for independent detection of Al3+
2
+
[
25-27] or Cu [28, 29] have been reported comprehensively on employing the
fluorescent or colorimetric mechanism. Yet, fluorescent or colorimetric probes for
3
+
2+
simultaneous differential detection of Al or Cu in aqueous media are still minor
30-34]. Herein, in this paper, we have designed and developed a dual functional
probe based on chromone derivative (L). It could selectively and sensitively detect
[
3
+
2+
both Al and Cu by different responses like fluorescent and colorimetric. At this
point, it was observed that L exhibited highly selective colorimetric and fluorescent
2
+
3+
3+
sensing capabilities for Cu and Al respectively. When added with Al ion, L
displayed a turn on green fluorescence in EtOH/H O (3/2) aqueous media.
2
2+
Furthermore, toward Cu , probe L displayed a colorimetric differentiation with color
transferred from colorless to yellow.
4

Experimental
Materials and instruments
All solvents and reagents used in the experiment are purchased by commercial
suppliers and could be used without further purification. In the experiments double
distilled water was used. The high-resolution mass spectrum was recorded on a
1
Bruker esquire 6000 spectrometer. H NMR measurements were conducted on a
JNM-ECS 400 MHz. UV–vis absorption and fluorescent spectrum were determined
on a Shimadzu UV-240 and a Hitachi RF-4500 spectrophotometer respectively. All
pH measurements were acquired by PHS-3C digital pH-meter. The pH meter was
calibrated before each titration experiment.
Synthesis of L
6
-ethoxychromone-3-carbaldehyde (compound 1 M.P.: 132-133℃) and furanyl
hydrazid e（ M.P.:73-74℃）were prepared according to the literature method previously
35, 36]. Based on the following steps, probe
[
6
-ethoxychromone-3-carbaldehyde-(furanyl)hydrazone（L）was synthesized (Scheme
1
): The solution of furan-2-carbohydrazide (0.0630 g, 0.5 mmol) in acetonitrile (10
mL) was added to another solution including compound 1 (0.1091 g, 0.5 mmol) in
acetonitrile (10 mL). After that, the stirred solution could reflux for 24 h and the
solvent was removed in vacuo. When it was cooled to room temperature, a brown
solid precipitated and was filtered and washed 5 times with acetonitrile. Then dried to
1
give a light brown solid in 54% yield. M.P.: 186-187℃. H NMR (400 Hz, DMSO-d
6
,
8
11
TMS) (Fig. S1): δ ppm 11.95 (s, 1H, H ), 8.81 (d, 1H, J = 10 Hz, H ), 8.63(s, 1H,
H
7
6
4
9
H ), 7.95 (s, 1H, H ), 7.69 (d, 1H, J = 7.69 Hz, H ), 7.47 (d, 1H, J = 9.2 Hz, H ),
3
5
10
7
.44(t, 1H, J = 9.2 Hz, H ), 7.33 (s, 1H, H ), 6.71 (m, 1H, H ), 4.15 (q, 1H, J = 6.8
2
1
13
Hz, H ), 1.38 (t, 3H, J = 6.8 Hz, H ). C NMR (400 Hz, DMSO, TMS) (Fig. S2): δ
C
ppm 174.72, 156.30, 154.35, 154.14, 150.48, 146.48, 146.07, 140.60, 124.15, 124.07,
5

1
20.40, 117.53, 115.03, 112.15, 105.51, 63.82, 14.56. The high-resolution mass
spectrum (HRMS) of L was shown in Fig. S3 and the peaks at m/z = 327.10 could be
+
+
+ +
assigned to [L + H ] and the peaks at m/z = 349.08 could be assigned to [L + Na ] .
Spectroscopic measurements
-3
The 5 × 10 M stock solutions of their chloride or nitrate salts of various metal
+
2+
2+
2+
2+
3+
2+
3+
2+
+
2+
2+
+
2+
ions (Ag , Ba , Ca , Cd , Co , Cr , Cu , Fe , Hg , K , Mg , Mn , Na , Ni ,
2
+
2+
3+
Pb , Zn , and Al ) were prepared in EtOH. Stock solution of compound L was
-3
prepared for using EtOH as a solvent with the concentration of 5 × 10 M. 2 mL
EtOH/HEPES solution (3/2, 20.0 μM HEPES solution, pH 7.24) was put into the
cuvettes. 20 μL L probe solution and a series of different metal ion solutions (1.0
equiv.) were added to make the final concentration of 50.0 μM. For all fluorescent
measures, the spectrums were set at an excitation wavelength of 420 nm and an
emission wavelength of 497 nm in EtOH/H O aqueous buffer solution. The widths of
2
excitation and emission slit were set at 5 nm. For all absorption measurements, the
test solutions were also made by the above means. After mixing them for several
seconds, UV-vis spectrum was carried out at room temperature.
Results and discussion
Effect of solvent and time
Solvents have a large effect on the fluorescence response of the probe, and the
selectivity varies depending on the solvent. In order to investigate the effect of
solvents on the optical properties of L, we recorded the fluorescence changes of L
3
+
after adding Al in different solvents. It could be seen from the Fig. 1a. that the
3
+
fluorescence intensity enhancement of the L-Al system was the most remarkable in
ethanol. However, for practical purpose, water which is more environmental friendly
and applies more widely. We choose a co-solvent system of ethanol and water as the
working solution. It was observed that the fluorescence intensity in mixed aqueous
6

media (EtOH/H
results are shown in Fig. 1b. Amusingly, the fluorescence intensity of L achieved the
strongest when the water fraction of the binary solvent mixture (EtOH/H O) was 40%.
Therefore, we chose EtOH/H O (3/2) as the testing solvent for optical properties
research. The effect of response time was conducted for the fluorescence intensity of
2
O) by varying volume of water percentages progressively and the
2
2
3
+
3+
L-Al . As shown in Fig. S6, when Al was added, the fluorescence intensity at 497
nm increased rapidly for 20 min and reached its maximum in 30 min, maintained a
stable state for more than 35 min. The results shown that this sensor L could be used
3
+
for real-time detection of Al .
Fluorescence and UV–vis spectroscopic studies of probe L for metal
ions sensing
Fig. 2a shown the fluorescence changes of L by photoirradiation in EtOH/H
3/2, 20.0 μM HEPES solution, pH 7.24) at room temperature. When the excitation
wavelength was set at 420 nm, L only exhibited weak fluorescence emission in the
2
O
(
3
+
range of 450-600 nm. However, when Al was added, the absorption intensity at 497
nm increased sharply. The addition of other metal ions made the fluorescence changes
2
+
very restricted except Zn , which led to the enhancement of fluorescence to a certain
extent. Subsequently, the changes of fluorescence spectrum were observed under the
irradiation of hand-held ultraviolet lamp (365nm). There is no obvious fluorescence in
the free L, and light green fluorescence produced immediately upon interaction with
3
+
Al . These visual fluorescence changes were not observed in the addition of other
metal ions (Fig. 2b). Fluorescence detection showed that L had an outstanding
3
+
selectivity to Al in aqueous medium.
2
+
As shown in Fig. 3a, the presence of Cu to L resulted in an immediately color
changed from colorless to yellow. It indicated that probe L could be applied as a
2
+
"
naked eye" probe to detect Cu in aqueous solution. Interestingly, the UV–visible
absorbance spectrum of probe L (50.0 μM) in EtOH/H O (3/2, 20.0 μM HEPES
2
7

solution, pH 7.24) at room temperature revealed few absorbance at the range from
80 nm to 480 nm (Fig. 3b). However, a strong absorption peak appeared at 422 nm
3
2
+
after the addition of Cu ion probably due to the happening of the strong coordination
2
+
between probe L and Cu . On the contrary, L showed little or no changes in
absorption peaks and color upon the addition of other cations.
Effect of pH
To verify the pH effect, we also estimated the effect of pH on the emission bands
3
+
2+
of L, the L-Al complex and the L-Cu complex in EtOH/H
2
O (3/2). The effect of
3
+
pH on the fluorescence spectrum of L and L-Al was investigated in Fig. 4a. When
3
+
pH value was lower than 4, the fluorescence intensity of L and L-Al was low with
3
+
no significant difference. A highly sensitive response of L toward Al could be
observed in the pH range of 4-8. When the pH was greater than 9, the fluorescence
intensity decreased significantly, which may be related to the formation of Al(OH) −
4
3
+
[
37]. This finding demonstrates that L could detect Al in a physiological pH range.
2
+
The influence of pH value on the absorbance of L and L-Cu complex was
investigated. As shown in Fig. 4b, L exhibited weak absorbance throughout the pH
2
+
range (3-11). Nevertheless, with the addition of Cu , the pH of aqueous solution had
2
+
a significant effect on the absorption intensity of the L-Cu . When the pH value of
2
+
the medium was below 6, the absorption intensity of the L-Cu complex decreased,
reaching a minimum at pH = 3. At high pH (> 11), and the intensity of absorption
gradually decreased due to the formation of insoluble Cu(OH) . Therefore, the probe
2
2
+
L could be applied as a colorimetric probe for Cu with naked eye recognition in the
pH ranging from 6 to 10.
Competition experiment
To further explore the practicability of probe L, competition experiments were
conducted. The probe L solution was mixed with other metal ions in the presence of
3
+
2+
2+
Al ions. Interestingly, except for Cu and Fe , other metal ions have a few
8

2
+
interference effects with the fluorescence emission intensity (Fig. 5a). For Cu and
2
+
Fe , the magnetic properties of the metal ion led to the electron and energy
transferred from ligand to the metal ion, resulting in the obvious decrease of the
fluorescence emission intensity at 497 nm. In addition, the receptor L was treated
2
+
with 1.0 equiv. Cu and 1.0 equiv. of other metal ions. At last, in EtOH/H
2
O (3/2,
2
0.0 μM HEPES solution, pH 7.24), it was observed that other metal ions did not
2
+
interfere with the detection of L towards Cu (Fig. 5b). Therefore, L could be used as
3
+
not only a selective fluorescent probe for the detection of Al , but also an excellent
2
+
chromogenic sensor for the detection of Cu in the presence of other metal ions.
Titration studies of probe L with metal ions
The fluorescence titration experiments were performed with different
3
+
3+
concentrations of Al ions. As shown in Fig. 6a, upon the gradual addition of Al
ion, the emission intensity of the peak at 497 nm significantly enhanced. Furthermore,
3
+
the emission intensity at 497 nm was linearly related to the concentration of Al in
2
the range of 0.0 - 1.0 equiv., and the correlation coefficient is R = 0.999 (Fig. S7).
The phenomenon displayed that the probe L was appropriate for the quantitative
3
+
−7
evaluation of Al ions. The detection limit was computed to be 1.801 × 10 M on the
basis of the definition by IUPAC (3σ/k), where the calculated value of σ was 1.082.
According to the ratio slope of the corresponding linear relationship in
Benesi-Hildebrand E
q
. (1) [38, 39], the correlation constant K
of the complex L-Al3+
a
4
−1
can be calculated, which was 2.618 × 10 M (Fig. S8).
1
1
1
=
ꢀ
+
3
퐹 − 퐹0 퐾푎(퐹푚푎푥 − 퐹 )[퐴푙 ]
퐹
− 퐹0
0
푚푎푥
Among them, Fmax, F and F respectively represented the fluorescence intensity at 497
0
3
+
3+
nm in the presence of saturated Al , arbitrary intermediate Al concentration and
free sensor L.
2
+
The binding properties of L and Cu were investigated by UV-visible titration
2
+
(
Fig. 6b). With the addition of Cu , the absorption band at 319 nm gradually
decreased and the new absorption band at 422 nm increased. Moreover, the color of
9

solution changed rapidly from colorless to yellow. The United States Environmental
Protection Agency (EPA) and the World Health Organization (WHO) have drafted the
2
+
−6
−6
maximum pollutant levels of Cu in drinking water at 20 × 10 M and 31 × 10 M,
respectively [41, 42]. According to the definition of IUPAC (3σ/k), the calculated
−7
value of σ was 0.0023 and the detection limit of L is 2.857 × 10 M, which was
much lower than the maximum pollution limit of drinking water [43-45] (Fig. S9).
The ratio slope of the corresponding linear relationship of the Benesi–Hildebrand
equation E
q
. (2) [46] was used to calculate the association constant K of the complex
a
2
+
5
−1
L-Cu , which is 2.225 × 10 M (Fig. S10).
1
1
1
=
ꢀ
+
2
퐴 − 퐴0 퐾푎(퐴푚푎푥 − 퐴 )[퐶푢 ] 퐴푚푎푥 − 퐴0
0
Among them, Amax, A, and A
0
represented the absorption at 422 nm in the presence of
2
+
2+
saturated Cu , arbitrary intermediate Cu concentration and free sensor L, severally.
The LOD values given for L were lower or in the same range compared to formerly
3+
2+
reported Al fluorescence and Cu colorimetric probes (Table 1).
Proposed sensing mechanism
3
+
The mode of association between L and Al was determined by high-resolution
mass spectrum (HRMS) (Fig. S4). Mass spectrometry indicated that the peak of m/z =
3
+
+
+ +
4
11.08 can be attributed to the [L + Al + 2H
2
O + CH
3
CH OH - H - Na ] complex
2
3
+
and the peak of m/z = 457.12 can be attributed to the [L + Al + 2H
2
O +2
+
+
+
3+
CH
3
CH
2
OH - H - Na ] complex. To farther affirm the binding mode of L and Al ,
Job’s plot (Fig. 7a) analysis was performed based on the fluorescence emission
spectrum. The Job’s plot showed a 1:1 complexation that was formed for the L-Al3+
complex. To investigate further information about the coordination mode of L-Al3+
3
+
1
1
complex, we have used Al to perform H NMR titration of L. The H NMR spectra
3
+
of the L and L-Al were measured in DMSO-d
6
(Fig. 8). By comparing them, it could
7
8
11
be found that the proton signal peaks of H , H and H were moved to the downfield
by 0.181 ppm, 0.014 and 0.438 ppm, respectively. These chemical shifts indicated that
N on imine, O on carbonyl group of furan amide and O on carbonyl group of
10

3
+
chromone might be involved in the coordination between L and Al . The lone pair
electrons from the Schiff-base nitrogen atom and oxygen atom of 6-ethoxychromone
contributed to the photoinduced electron-transfer (PET) phenomenon [50–52], which
electrons from the imine nitrogen were transferred to the aromatic ring and
fluorescence quenched. Then the quenched fluorescence could increase dramatically
upon chelating metal ion by inhibiting the PET processes. Therefore, a strong
3
+
fluorescence enhancement was observed at 497 nm with adding Al , which was
because that the formation of a 1 : 1 ligand-metal complex restricted the PET process.
Simultaneously, as shown in Fig. S5 and Fig. 7b, we have conducted HRMS spectrum
2
+
+ +
and Job’s plot. Based on the HRMS spectrum, the peak of [L + Cu - H ] appeared
2
+
at m/z = 388.01 after addition of Cu (Fig. S5). The Job's plot was investigated by the
2
+
absorption spectrum. It was found that fluorescence intensity of L-Cu complex
arrived the maximum when molar fraction was 0.5, which expressed the binding
2
+
stoichiometry between L and Cu was 1 : 1. However, on account of the Job’s plot,
1H NMR titration and high-resolution mass spectrum analysis, the proposed
3
+
2+
mechanisms for the detection of Al and Cu by L were illustrated in Scheme 2.
Analytical application of L
-2
-3
-4
-5
-6
-7
2+
Different concentrated solutions (10 , 10 , 10 , 10 , 10 , 10 , 0 M) of Cu
were prepared in EtOH/H O (3/2, 20.0 μM HEPES solution, pH 7.24) in glass vials
and 5× 10 M of L was added to each bottle and pictures were taken under room
2
−3
2
+
light (Fig. 9). Depending on the concentration of Cu in the vial, the color of the
mixture in each vial changed from colorless to pale yellow or yellow, which could
-6
2+
easily observed by the naked eye. As shown in Fig. 9, bottle containing 10 M Cu
2
+
can be visually observed by naked eye while the WHO permitted level of Cu in
−6
drinking water is 31 × 10 M. Therefore, these results indicated that L could be
2
+
applied as a colorimetric probe for Cu by naked-eye recognition.
3
+
Experiments for detection of Al were conducted on silica coated slides. In the
3
+
experiment, some L solution was added to a piece of silica gel, while L and Al were
11

3+
added on the other side. Interestingly, after interacted with Al , the probe adsorbed on
the silica coated slide showed an immediate fluorescent color change from dark blue
to light green under 365 nm ultraviolet light (Fig. 10a).
2
+
Enlightened by the change in the apparent coloration of L in the presence of Cu ,
2
+
the practical usability of L as a solid-state probe for Cu detection was checked. To
this end, the filter paper was immersed in EtOH: H O (3 : 2, v/v) solution of L (0.5
2
mM) and then dried in air to adsorb L on the filter paper. Whereafter, various metal
ions (0.5 mM) solutions were dripped onto the test strip. As shown in Fig. 10b, under
the visible light, the color of the coated test paper was changed from white to yellow
2
+
by the adding of Cu . However the color of the test paper coated with the other metal
ions did not change obviously.
Conclusion
In conclusion, we have developed a novel and easily available fluorescent probe
3
+
L based on a chromone skeleton which is a dual probe capable of detecting Al and
2
+
3+
Cu . L displayed excellent selectivity for Al via a turn-on fluorescence change and
2
+
for Cu through the naked-eye by a color change from colorless to yellow in
EtOH/H
O (3/2, 20.0 μM HEPES solution, pH 7.24). The detection limit of L for Al3+
2
−7
2+
−7
is 1.801 × 10 M and for Cu is 2.857 × 10 M which is adequately low in
comparison to the standard of WHO and EPA lays the foundation for valid detecting
of both the cations in real samples. In addition, L could work over a wide range of pH
3
+
2+
3+
span and might be used to living cells for detecting Al and Cu . Moreover, L-Al
2
+
and L-Cu were coordinated with a 1:1 ratio which validated by the Job’s plot, HRMS
1
3+
and H NMR. Choosing recognition of L to Al should be due to the interaction
3
+
between chromone skeleton and Al , which inhibited the PET process. Besides, the
2
+
selective recognition of Cu could be attributed to the colorimetric method. What's
more, in the solid state, L also had an excellent sensing performance. Based on these
results, we believe that probe L can be a prototype for many practical applications in
environmental and biological systems.
12

Acknowledgments
This work is supported by the National Natural Science Foundation of China
(
21761019).
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16

1000
a
900
800
700
600
500
400
300
200
100
0
acetonitrile
acetone
DMF
DMSO
water
ethyl acetate
methanol
ethanol
450
500
550
600
650
Wavelength (nm)
900
800
700
600
500
400
300
200
100
0
b
1
2
30%
4
5
60%
7
8
90%
0%
0%
0%
0%
0%
0%
450
500
550
600
650
Wavelength (nm)
3
+
Fig. 1. (a) Solvent effect on fluorescence intensity of the probe L, with Al in
different solvent; (b) Fluorescence spectra of L in EtOH, upon increasing the volume
of water percentages from 10% to 90%.
17

900
800
700
600
500
400
300
200
100
0
a
3
+
Al
2+
Zn
L + other ions
450
500
550
600
650
Wavelength (nm)
Fig. 2. (a) Fluorescence emission spectrum of L (50.0 μM) upon addition of various
+
3+
2+
2+
2+
2+
3+
2+
3+
2+
+
metal ions (1.0 equiv.) (Ag , Al , Ba , Ca , Cd , Co , Cr , Cu , Fe , Hg , K ,
2
+
2+
+
2+
2+
2+
2+
Mg , Mn , Na , Ni , Pb , Zn and Fe ) in EtOH/HEPES solution (3/2, 20.0 μM
HEPES solution, pH 7.24) (λex = 420 nm, slit widths: 5 nm/5 nm) ; (b) The
photograph of L after addition of different metal ions under illumination using a 365
nm UV lamp.
18

b 1.25
1
0
0
0
0
.00
.75
.50
.25
.00
2
+
Cu
L + other ions
325
350
375
400
425
450
475
500
Wavelength (nm)
Fig. 3. (a) The photograph of L after addition of different metal ions under the visible
light; (b) Absorption changes of L (50.0 μM) upon addition of various metal ions (1.0
+
3+
2+
2+
2+
2+
3+
2+
3+
2+
+
2+
2+
+
equiv.) (Ag , Al , Ba , Ca , Cd , Co , Cr , Cu , Fe , Hg , K , Mg , Mn , Na ,
2
+
2+
2+
2+
Ni , Pb , Zn and Fe ) in EtOH/HEPES solution (3/2, 20.0 μM HEPES solution,
pH 7.24) (λex = 420 nm, slit widths: 5 nm/5 nm).
19

900
800
700
600
500
400
300
200
100
0
a
L
3
+
L + Al
1
2
3
4
5
6
7
8
9
10 11
pH
0
.9
.8
.7
.6
.5
.4
.3
.2
.1
.0
b
L
0
2+
L + Cu
0
0
0
0
0
0
0
0
-0.1
2
3
4
5
6
7
8
9
10 11 12
pH
Fig. 4. (a) Variation of fluorescence intensity at 497 nm of L (50.0 μM) in EtOH/H O
2
3
+
(
3/2) solution with and without Al (1.0 equiv.) as a function of pH; (b) Variation of
absorbance at 422 nm of L (50.0 μM) in EtOH/H O (3/2) solution with and without
2
2
+
Cu (1.0 equiv.) as a function of pH.
20

a
other ions
900
800
700
600
500
400
300
200
100
0
3
+
other ions + Al
3+
+
2+
2+
2+
2+
3+
2+
3+
2+
+
2+
2+
+
2+
2+
2+
ee
Fr Al
2+
K
Na Ni Pb Zn Fe
Ag Ba Ca Cd Co Cr Cu Fe
Hg
Mn Mg
3
+
Fig. 5. (a) Fluorescence emission intensity of L and its complexation with Al in the
presence of other various metal ions in EtOH/HEPES solution (3/2, 20.0 μM HEPES
solution, pH 7.24) (λex = 420 nm, slit widths: 5 nm/5 nm). Black bar: L (50.0 μM) in
+
3+
2+
2+
2+
2+
3+
2+
3+
2+
the presence of 1.0 equiv. of Ag , Al , Ba , Ca , Cd , Co , Cr , Cu , Fe , Hg ,
+
2+
2+
+
2+
2+
2+
2+
K , Mg , Mn , Na , Ni , Pb , Zn and Fe . Red bar: L (50.0 μM) with 1.0 equiv.
3
+
of Al in the presence of 1.0 equiv. of other various metal ions (λex = 420 nm); (b)
2+
The color changes of competitive selectivity of L (50.0 μM) toward Cu (1.0 equiv.)
in the presence of other metal ions (1.0 equiv.) in EtOH/HEPES solution (3/2, 20.0
μM HEPES solution, pH 7.24).
21

900
800
700
600
500
400
300
200
100
0
a
1
.0 equiv.
0
.0 equiv.
450
500
550
600
650
Wavelength (nm)
b
1
.4
.2
.0
.8
.6
.4
.2
.0
1
.0 equiv.
1
1
0
0
0
0
0
0
equiv.
250
300
350
400
450
500
Wavelength (nm)
Fig. 6. (a) Fluorescence emission spectrum of L (50.0 μM) in EtOH/HEPES solution
3
+
(
3/2, 20.0 μM HEPES solution, pH 7.24) upon gradual addition of Al (0 - 1.0 equiv.)
ex = 420 nm, slit widths: 5 nm/5 nm); (b) UV-vis absorption spectrum of L in
(
λ
EtOH/HEPES solution (3/2, 20.0 μM HEPES solution, pH 7.24) after addition of
2
+
Cu (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 equiv.).
22

350
300
250
200
150
100
a
50
0
0
.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
XAl
b
0
0
0
0
0
0
0
0
.50
.45
.40
.35
.30
.25
.20
.15
0
.0
0.2
0.4
0.6
0.8
1.0
XCu
3
+
Fig. 7. (a) Job’s plot for determining the stoichiometry between L and Al in
EtOH/HEPES solution (3/2, 20.0 μM HEPES solution, pH 7.24) at 497nm. XAl
=
3
+
3+
3+
[
Al ]/ ([Al ] + [L]), the total concentration of L and Al was 50.0.0 μM (λex = 420
2
+
nm, slit widths: 5 nm/5 nm); (b) Job plot for the binding of L with Cu . Absorbance
2
+
2+
at 442 nm was plotted as a function of the molar ratio [Cu ]/ ([Cu ] + [L]), the total
2
+
concentration of L and Cu was 50.0.0 μM.
23

1
3+
Fig. 8. H NMR spectra in DMSO-d6: above: L only; below: Al and 1.0 equiv. of L
24

2
+
Fig. 9. Naked eye color response of L towards different concentrations of Cu .
Picture was taken under room light.
25

Fig. 10. (a) The photograph of silica coated slides. (1) was just added L and (2) was
3
+
added L and Al , both (1) and (2) were taken under the 365 nm UV lamp; (b) The
photograph of coated test paper after addition of different metal ions under the visible
light.
26

Scheme1. Synthetic route of L.
3
+
2+
Scheme 2. Proposed mechanisms for the detection of Al and Cu by L.
27

2
+
3+
Table 1. Comparison of probes for Cu /Al detection.
−
1
Media
MeCN/H
EtOH
LOD (M)
Al3+
Ka (M )
Applicatio Ref.
n
Cu2+
Al3+
Cu2+
2
O (2:3)
7.32 × 10-8
1.47 × 10-8 3.95 × 103 2.74× 1011
M−2
Cell image
[30]
1.0 × 10−9
NM
1.83 × 104 NM
No
[31]
[47]
MeOH/H
2
O(2:1) Al 1.26 × 10-8
O(2:1) Cu
1.84 × 10-8 1.23 × 105 1.32 × 105
Cell image
MeCN/H
MeCN/H
2
2
O (1:1)
2.25 × 10-8
1.06 ×10−7 1.01 × 105 5.50 × 104
Cell image
Cell image
[48]
[49]
MeOH/PBS(95:5)Al 3.1 × 10−7
MeOH/Tris(4:6) Cu
5.4 × 10−7 2.61 × 105 5.84 × 104
EtOH/H
2
O (3 : 2)
1.80 ×10−7
2.86×10−7 2.61 × 104 2.23 × 105
as a solid
This
state probe
work
LOD: The limit of detection; NM: Not mentioned in the corresponding paper.
28