A novel dual-responsive fluorescent probe for the detection of copper(II) and nickel(II) based on BODIPY derivatives

Article abstract of DOI:10.1016/j.ica.2020.120099

A novel dual-responsive fluorescence probe 6 was constructed by introducing a dipicolyamine moiety on the BODIPY-based skeleton via Sonogashira coupling reaction and confirmed by ¹H NMR, ¹³C NMR, elemental analysis and high-resolution mass spectroscopy (HRMS). The present probe 6 exhibited high selectivity and sensitivity toward Cu²⁺ and Ni²⁺ detection over other competitive metal ions by fluorescence quenching phenomena, respectively. In addition, the detection limits (DLs) for Cu²⁺ and Ni²⁺ were calculated to be as low as both 0.1 μM respectively, which were lower than the maximum allowable level of the World Health Organization (WHO) limit for the drinking water. The stoichiometric ratio of the probe 6 toward the Cu²⁺ or Ni²⁺ ions was determined to be 1:1 according to the result of the Job's plot and HRMS analysis. These results indicated that probe 6 can be used as a selective ‘‘turn-off’’ fluorescent sensor for the detection of Cu²⁺ and Ni²⁺.

Full text of DOI:10.1016/j.ica.2020.120099

Inorganica Chimica Acta xxx (xxxx) xxx
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
A novel dual-responsive fluorescent probe for the detection of copper(II)
and nickel(II) based on BODIPY derivatives
,
,
,
Yuting Songa 1, Jiayu Taoa 1, Yi Wanga, Zhengchun Caia, Xianying Fanga *, Shifa Wanga,
,b,*
Haijun Xua
a Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037,
China
b School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang 453002, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
BODIPY
DPA
A novel dual-responsive fluorescence probe 6 was constructed by introducing a dipicolyamine moiety on the
BODIPY-based skeleton via Sonogashira coupling reaction and confirmed by 1H NMR, 13C NMR, elemental
analysis and high-resolution mass spectroscopy (HRMS). The present probe 6 exhibited high selectivity and
sensitivity toward Cu2+ and Ni2+ detection over other competitive metal ions by fluorescence quenching phe-
nomena, respectively. In addition, the detection limits (DLs) for Cu2+ and Ni2+ were calculated to be as low as
Fluorescence sensor
Cu2+
Ni2+
both 0.1 μM respectively, which were lower than the maximum allowable level of the World Health Organization
(WHO) limit for the drinking water. The stoichiometric ratio of the probe 6 toward the Cu2+ or Ni2+ ions was
determined to be 1:1 according to the result of the Job’s plot and HRMS analysis. These results indicated that
probe 6 can be used as a selective ‘‘turn-off’’ fluorescent sensor for the detection of Cu2+ and Ni2+
.
1. Introduction
significant environmental pollutant due to the lack of effective man-
agement deriving from its widespread use in current agriculture and
industry. [12,15] On the other hand, Nickel is also an essential trace
element for a variety of enzymes in biological systems such as respira-
tion, biosynthesis, and metabolism. [16,17] However, the excessive
uptake of Ni2+ in the human body can cause various diseases, such as
asthma, acute pneumonitis, dermatitis, and cancer of the lung and sinus.
[18] Besides, Ni2+ is also a significant environmental pollutant as one of
the heavy metals. Consequently, the development of highly sensitive
and selective analytical methods for the detection of Cu2+ and Ni2+ is of
great importance for the human health and environment. In the past few
years, various analytical methods have been applied for the determi-
nation of Cu2+ and Ni2+ ions. [12,19,20] Compared to those methods,
the fluorescence probe has drawn considerable attention due to its good
selectivity, high sensitivity, operational simplicity, fast response time,
and low cost. [12,21–28] In recent years, a number of fluorescent probes
for the detection of Cu2+ and Ni2+ have been reported, such as
coumarin, 1,8-naphthalimide, rhodamine and fluorescein, which show
Selective and sensitive detection of various heavy metal ions has
received increasing attention due to their significant importances in
bioanalysis and environmental monitoring. [1,2] Among these metal
ions, copper ion (Cu2+) is the third most abundant metal ion after iron
and zinc in the human body, which plays important and indispensable
roles in physiological and pathological processes such as respiration,
enzyme functions, antioxidant defense, and gene expression. [2–5]
Trace amount of Cu2+ uptake is very necessary for the living system
towards growth and development. [6] An undersupply of these metal
ions leads to deficiency and oversupply results in toxic effects. [7]
However, the imbalance of Cu2+ level causes various diseases. [8]
Excessive concentration levels of Cu2+ in human body can exhibit
toxicity and result in many serious diseases such as kidney or liver
damage, Alzheimer’s disease, Wilson’s and Parkinson’s diseases and
even may cause death. [1,4,9–11] Also, deficiency of Cu2+ can cause
anemia, hair abnormalities, and arterial abnormalities, and also affect
the development of bones and brain. [12–14] In addition, Cu2+ is also a
high sensitivity and low detection limit toward Cu2+ and Ni2+
.
* Corresponding authors at: Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing
Forestry University, Nanjing 210037, China (H. Xu).
E-mail addresses: fxy_08@163.com (X. Fang), xuhaijun@njfu.edu.cn (H. Xu).
1
These authors equally contribute to this work.
https://doi.org/10.1016/j.ica.2020.120099
Received 28 July 2020; Received in revised form 18 October 2020; Accepted 20 October 2020
Available online 24 October 2020
0020-1693/© 2020 Elsevier B.V. All rights reserved.
Please cite this article as: Yuting Song, Inorganica Chimica Acta, https://doi.org/10.1016/j.ica.2020.120099

Y. Song et al.
Inorganica Chimica Acta xxx (xxxx) xxx
[1,17,29–32] However, some probes for Cu2+ and Ni2+ still are con-
fronted with some thorny problems, such as complicated synthetic
procedures, difficult purification, and strict testing conditions.
[26,31,33] In addition, to the best of our knowledge, there are only a few
reports that show a single fluorescence probe for recognizing both Cu2+
and Ni2+ simultaneously. [7,8,17,34–37] Therefore, it is still of a great
interest and necessary to develop highly sensitive and selective fluo-
rescence probes to detect and estimate the trace levels of Cu2+ and Ni2+
in the environment. [26,35,36,38]
1H NMR and high-resolution mass spectrometry and showed high
selectivity and sensitivity towards Cu2+ and Ni2+ in methanol media
compared to the other transition and toxic heavy metal ions.
2. Results and discussion
2.1. Synthesis of probe 6
The synthetic route of probe 6 was shown in Scheme 1. Probe 6 was
synthesized by the Sonogashira coupling reaction of BODIPY derivatives
2 with bis(pyridin-2-ylmethyl)amine derivatives 5. The product of each
step of the synthesis has been characterized by 1H NMR spectroscopic
technique. The target product 6 was also characterized by HRMS. All the
detailed characterization data were presented in the Supporting Infor-
mation (Figs. S1–S7).
4,4-Difluoro-4-borato-3a,4a-diaza-s-indacene (BODIPY) derivatives
are one of the most important fluorescent dyes and possess excellent
photophysical and optoelectronic properties, such as high photo-
stability, large absorption coefficient in the visible and near-IR ranges,
excellent chemical stability, sharp absorption and fluorescence bands,
and high fluorescence quantum yields. [39–41] Also, the spectroscopic
and photophysical properties of the BODIPY derivatives can be tuned by
appropriate substitution. [42–45] Furthermore, the parent structure of
the BODIPY dyes is easily modified on all possible positions of the core,
and various functional groups can be introduced to the BODIPY core for
different applications. [46–48] As a result, the BODIPY dyes are widely
used for the design and synthesis of fluorescent probes for detecting
different ions. [49–53] For example, a few fluorescent probes for
detecting Cu2+ were constructed by integrating bis(pyridin-2-ylmethyl)
amine (DPA) to the 3-position of BODIPY fluorophore. [45,54,55] Also,
substitution at the 2- and/or 6-position(s) on the BODIPY core can cause
significant shifts in the absorption and fluorescence spectra. [49,56]
However, few studies have been conducted on substituent effects at the
2- and/or 6-position(s) of BODIPY to obtain metal ion probes. [49,57]
Herein, we have now synthesized a new ratiometric fluorescent probe 6
by the introduction of a cation receptor DPA at the 2-position of BODIPY
core, which can act as a dual chemosensor for selective/sensitive
response to cations Cu2+ and Ni2+. The probe 6 was confirmed by using
2.2. Selectivity detection studies of 6 towards various metal ions
The sensing abilities of the probe 6 towards various biologically and
environmentally affected ions such as Zn2+, Ni2+, Cd2+, Cu2+, Pd2+
,
Fe3+, Mn2+, Mg2+, K+, Na+, Cr3+, Ag+, Hg2+, and Co2+ were investi-
gated in methanol by UV–Vis absorption and fluorescence spectra.
Different metal ions (10 equiv.) were separately added into the solution
of probe 6 (1 × 10ꢀ 5 mol/L). As shown in Figure S8, the probe 6 shows
the typical maximum absorption wavelength of BODIPY at 542 nm
which is ascribed to S0 → S1 (π–π*) transition of BODIPY conjugated
system. [41] However, slight changes can be observed in the UV–Vis
absorption spectra in the presence of different ions (Fig. S8). As seen
from Fig. 1, different from the UV–Vis absorption spectra, the probe 6
shows considerable changes of the fluorescence intensity upon with the
addition of different metal ions. The probe 6 alone exhibited an intense
emission band at 589 nm with a quantum yield value of 0.065 upon the
Scheme 1. The synthetic route for 6.
2

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Fig. 1. Fluorescence emission spectra of probe 6 (1 × 10ꢀ 5 mol/L) and in the
presence of 11 kinds of metal ions such as Cu2+, Ni2+, Zn2+, Cd2+, Pd2+, Fe3+
,
Fig. 2. The selectivity of probe 6 in MeOH (1 × 10ꢀ 5 mol/L) for Ni2+ in the
Mn2+, Mg2+, K+, Na+, Co2+, Cr3+, Ag+ and Hg2+ (10.0 equiv) in methanol
solution. (Excitation wavelength: 542 nm).
presence of other metal ions (10 equiv.) (Zn2+, Cd2+, Pd2+, Fe3+, Mn2+, Mg2+
,
K+, Na+, Co2+, Cr3+, Ag+ and Hg2+). (excitation wavelength: 542 nm, emission
wavelength: 589 nm).
excitation at 542 nm, and the fluorescence lifetimes were determined to
be 3.98 ns. The addition of the Cu2+ and Ni2+ ions to the methanol so-
lution of probe 6 resulted in a remarkable fluorescence quenching at the
wavelength of 589 nm; and the addition of Zn2+, Cd2+, and Pd2+ caused
a prominent fluorescence enhancement, and slightly quenched or no
fluorescence spectral changes were observed upon the addition of other
metal ions under the same conditions. The observed fluorescent
quenching might be attributed to the excited state electrons of probe 6
transfer to the unoccupied 3d orbital of Cu2+ or Ni2+. [36] The signifi-
cant spectra changes suggested that probe 6 should be more sensitive to
the presence of Cu2+ and Ni2+ ions than other mentioned ions due to
their higher binding interaction with the chelator of probe 6 that
resulted in the formation of stable complexes between probe 6 and the
Ni2+ or Cu2+. [8,58] Consequently, the result clearly indicates that
probe 6 can be used as a fluorescent probe to detect the Ni2+ and Cu2+
.
In order to further explore the high selectivity of probe 6 for Cu2+
and Ni2+ sensing, competition experiments were carried out with other
competitive co-existing metal ions. Fig. 2 and Fig. 3 showed the fluo-
rescence emission of probe 6 (1 × 10ꢀ 5 mol/L) in the presence of both 10
equiv. Ni2+/Cu2+ and 10 equiv. other metal ions (Zn2+, Cd2+, Pd2+
,
Fe3+, Mn2+, Mg2+, K+, Na+, Cr3+, Ag+, Hg2+ and Co2+). This fluores-
cence quenching by the solutions of Cu2+ (Fig. 2) and Ni2+ (Fig. 3) in
methanol was not affected significantly by the presence of the other
metal ions. This result strongly revealed that the binding affinity be-
tween probe 6 and Cu2+ or Ni2+ was stronger than that between probe 6
and other metal ions. Therefore, this also indicated that the recognition
of Ni2+ and Cu2+ by probe 6 was hardly interfered by other coexisting
metal ions. Thus, the probe 6 can be used as a selective fluorescent
sensor for Cu2+ and Ni2+ ions over other competing metal ions in a
methanol solution.
Fig. 3. The selectivity of probe 6 in MeOH (1 × 10ꢀ 5 mol/L) for Cu2+ in the
presence of other metal ions (10 equiv.) (Zn2+, Cd2+, Pd2+, Fe3+, Mn2+, Mg2+
,
K+, Na+, Co2+, Cr3+, Ag+ and Hg2+). (excitation wavelength: 542 nm, emission
wavelength: 589 nm).
incremental addition of a solution of the metal ion (Ni2+ or Cu2+) into
the solution of the probe 6, and then reached minimum and remained
almost constant after the addition of 1.0 equiv. of Cu2+ or Ni2+
,
respectively, which suggests the formation of 1:1 complexes between
probe 6 and either metal ion. Based on the concentration-dependent
experiments, a good linearity relationship between the fluorescence
intensities and the metal ion concentration of Cu2+ or Ni2+ in the range
of 0–1.0 equiv. was obtained, which were shown in Figs. 6 and 7
respectively. The regression equations were y = -429.818x + 707 (R2 =
0.984) for Cu2+ and y = 354.583x + 690 (R2 = 0.987) for Ni2+, where y
referred to the fluorescence emission intensity and ×x referred to the
concentration of Ni2+or Cu2+. Furthermore, the detection limit (DL)
2.3. Titration analysis probe 6 with Cu2+ and Ni2+
To get a better insight into the sensitive response of probe 6 towards
Ni2+ and Cu2+, titration experiments between probe 6 and the metal
ions (Ni2+ and Cu2+) were also performed in methanol by fluorescence
spectra. A methanolic solution of probe 6 (1 × 10ꢀ 5 mol/L) was titrated
with Cu2+ (0–1 equiv.) or Ni2+ (0–1 equiv.) solutions in methanol. The
changes in the fluorescence intensity as a function of the concentration
of Cu2+ and Ni2+ ions were shown in Figs. 4 and 5, respectively. The
fluorescence intensity gradually decreased at 589 nm with the
values for Cu2+ and Ni2+ were calculated to be both 0.1
μM,
3

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Fig. 4. Fluorescence emission spectra of probe 6 (2 × 10ꢀ 5 mol/L, excitation
Fig. 7. Calibration curve of 6-Cu2+ (emission wavelength: 589 nm).
wavelength: 542 nm) in MeOH upon addition of 0–1 equiv. of Ni2+
.
respectively, which were determined reasonably by the equation DL =
3σ/K. [8] Moreover, these detection limits were significantly lower than
the permitted levels of Cu2+ (30
μ
M) and Ni2+ (17
μM) in drinking water
set by the World Health Organization (WHO). [8,59] The result indi-
cated that the probe could be used as an excellent fluorescent sensor for
the recognition and detection of the Cu2+ and Ni2+ in biological and
environmental systems.
In addition, to further determine the binding stoichiometry between
probe 6 and Cu2+ or Ni2+, Job’s plot titration experiments of probe 6
with Cu2+ and Ni2+ and HRMS mass spectral analysis were carried out.
As shown in Fig. S9 and S10, the maximum point was measured at a
molar fraction of ca. 0.5, indicating the formation of a complex between
probe 6 and Cu2+ or Ni2+ in a 1:1 ratio. In the HRMS spectra (Fig. S11
and S12), the formation of a 1:1 complex between probe 6 and Ni2+ or
Cu2+ was confirmed by the emergence of the peak at m/z = 801.1256
[probe 6 + Cu2+ + Clꢀ ]+ or 820.1774 [probe 6 + Ni2+ + CH3CO–2]+. The
results obtained from the mass spectral analysis correlated well with
those obtained by the Job’s method. Therefore, based on the fluores-
cence titration experiments, HRMS, and Job’s plot analysis, the possible
binding mechanism between probe 6 and Cu2+ or Ni2+ was provided in
Scheme 2 [61–63]. The 1H NMR titration was also performed (Fig. S13).
However, no signal was observed after adding ions due to the formations
of paramagnetic Cu (II) and Ni (II) complexes. The FT-IR spectra for Cu
(II) complex, Ni (II) complex and probe 6 were presented in Fig. S15. The
Fig. 5. Fluorescence emission spectra of probe 6 (2 × 10ꢀ 5 mol/L, excitation
wavelength: 542 nm) in MeOH upon addition of 0–1 equiv. of Cu2+
.
–
C
N bond vibrations of pyridine in the corresponding Ni (II) and Cu (II)
–
complexes can be observed at 1606 and 1610 cmꢀ 1, respectively.
–
Compared with probe 6, the C N stretching frequency shifted to a
–
higher frequency by ca. 15 and 19 cmꢀ 1 for Ni (II) and Cu (II) complexes,
respectively, indicating forming the coordination bond between the
metal ion and the pyridine-N lone pair. Besides, the new stretching
frequency at 539 cmꢀ 1 for Ni (II) complexes and 509 cmꢀ 1 for Cu (II)
complexes can be attributed to v(Ni-N) and v(Cu–N), respectively. The
NMR titration and FT-IR spectra further confirmed the binding mecha-
nism between probe 6 and Cu2+ or Ni2+
.
3. Conclusion
In summary, a new ‘‘turn-off’’ dual responsive fluorescence chemo-
sensor containing BODIPY and DPA units for the detection of Cu2+ and
Ni2+ in a methanol solution was successfully synthesized and structur-
ally characterized by 1H NMR, 13C NMR, Esi-HRMS and elemental
analysis, which was investigated in detail by employing fluorescence
spectra. The investigations showed that probe 6 exhibits high selectivity
and sensitivity for the detection of Cu2+ and Ni2+ ions over several other
Fig. 6. Calibration curve of 6-Ni2+ (emission wavelength: 589 nm).
metal ions with the detection limit of as low as 0.1
μ
M for both Cu2+ and
4

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Inorganica Chimica Acta xxx (xxxx) xxx
Scheme 2. Proposed binding modes of probe 6 with Cu2+ and Ni2+ (L are solvent molecules or coordinating anions).
Ni2+. The 1:1 binding mode between probe 6 and the Cu2+ or Ni2+ ions
have been well demonstrated by HRMS spectra and Job’s method.
Therefore, the probe 6 is a dual-responsive and sensitive fluorescence
chemosensor for the detection of Cu2+ and Ni2+ ions and can be
potentially applied in various applications in the area of biology and
environment.
(81 mg, 0.36 mmol) were added into dry 30 mL of CH2Cl2 and stirred at
room temperature for 30 min. The reaction mixture was washed with
saturated aqueous Na2S2O3 (3 × 30 mL), dried over anhydrous Na2SO4,
and then concentrated under reduced pressure. The crude product was
purified by column chromatography on silica with CH2Cl2/petroleum
ether = 3:2 as the eluent, affording the desired compound 2. Yield (52.7
mg, 34%). 1H NMR (600 MHz, CDCl3, ppm), δ 7.47 (d, 3JH-H = 7.8 Hz,
2H), 7.40 (t, 3JH-H = 7.2 Hz, 1H), 2.65 (s, 3H), 2.59 (s, 3H), 1.51 (s, 3H),
1.49 (s, 3H). (Fig. S2)
4. Experimental section
4.1. Materials and measurements
4.2.2. Compound 6
Compound 5 (45 mg, 0.15 mmol), compound 2 (50 mg, 0.1 mmol)
and CuI (1.2 mg, 0.006 mmol) were dissolved in dry triethylamine (5
mL). The mixture was deoxygenated with argon, and then Pd(PPh3)4
(88 mg, 0.07 mmol) was added into the mixture under Ar. The reaction
mixture was heated at 80 ◦C for 12 h. After completion of the reaction,
the solvent was removed under reduced pressure and the crude product
was purified by column chromatography on silica gel with CH2Cl2/
CH3OH = 99.5:0.5 as the eluent, affording the desired compound 6.
Yield (21.7 mg, 43%). 1H NMR (600 MHz, CDCl3, ppm), δ 8.54 (d, 3JH-H
= 3.6 Hz, 2H), 7.70–7.65 (m, 4H), 7.58–7.54 (m, 3H), 7.50–7.45 (m,
3H), 7.40 (s, 3H), 7.19–7.17 (m, 2H), 6.06 (s, 1H), 3.92 (s, 4H), 3.80 (s,
2H), 2.70 (s, 3H), 2.60 (s, 3H), 1.60 (s, 3H), 1.50 (s, 3H). 13C NMR (150
MHz, CDCl3, ppm), δ 151.9, 148.4, 141.9, 136.7, 134.9, 130.5, 129.6,
127.7, 127.6, 125.8, 124.4, 124.2, 123.9, 123.6, 122.6, 121.7, 116.2,
115.4, 115.2, 114.0, 52.7, 50.7, 22.7, 9.0, 8.3, 7.9, 6.4. (Fig. S14). Anal.
Calcd. for C40H34BCl2F2N5(%): C, 68.20; H, 4.87; N, 9.94; Found(%): C,
68.24; H, 4.91; N, 9.91. HRMS (ESI): m/z calcd for C40H35BCl2F2N5 [M
+ H+]: 704.2325; found: 704.2348. (Fig. S7).
All chemicals and solvents were of analytical reagent grade and used
directly as received unless otherwise noted. Dry CH2Cl2 and triethyl-
amine was (TEA) were distilled from CaH2 under nitrogen. Dry tetra-
hydrofuran (THF) was distilled from sodium/benzophenone under
nitrogen. 1H NMR spectra were collected on a Bruker DRX-600 AVANCE
III spectrometer. Chemical shifts for 1H NMR spectra were recorded in
ppm relative to CDCl3 (δ = 7.26 ppm) as the internal standard. High-
resolution mass spectra data were obtained using a Thermo Fisher
LTQ Orbitrap XL (HR-ESI) spectrometer. UV–vis spectra were carried
out on a Shimadzu UV-3100 spectrophotometer. Fluorescent spectra
were recorded on a LS 55 Fluorescence Spectrometer (Perkin Elmer).
The PLQY were measured in FluoroLog-UltraFast (HORIBA Instrument
Inc, Edison) equipped with a 450 W CW xenon lamp and an Open-
Electrode TECooled CCD Detector (Syncerity). Nanosecond lifetime
was conducted using a TCSPC MCA model equipped with a picosecond
photo detector (<200 ps) (PPD850) and picosecond laser (duration is
180 ps, Deltadiode, 100 MHz laser). The fluorescence lifetime values
were obtained from deconvolution and distribution lifetime analysis. IR
spectra were recorded using a Bruker Vertex80 FT-IR spectrometer with
KBr discs in the range 400–4000 cmꢀ 1 range.
4.3. UV–vis and fluorescence titration
4.2. Synthesis of Compounds 1–6
Compound 6 (1.4 mg, 0.002 mmol) was dissolved in 100 mL MeOH
to form 2 × 10ꢀ 5 mol/L solution. CuCl2⋅2H2O (3.4 mg) and NiCl2⋅6H2O
(4.7 mg) were dissolved in 10 mL MeOH to form 2 × 10ꢀ 3 mol/L solu-
Compounds 1, 3, 4 and 5 were synthesized referring to the previ-
ously reported methods. [60 61] Detailed information can be found in
the supplementary data.
tion. 3 mL probe 6 solution was added into a cuvette, then 3
μL (0.1
equiv.), 6
equiv.), 18
(0.9 equiv.), 30
μ
L (0.2 equiv.), 9
μ
L(0.3 equiv.), 12
μ
L (0.4 equiv.), 15
μ
L(0.5
μ
L (0.6 equiv.), 21
μ
L (0.7 equiv.), 24
μ
L (0.8 equiv.), 27
μ
L
4.2.1. Compound 2
μ
L (1 equiv.) of Cu2+ or Ni2+ solution were added,
Compound 1 (117.92 mg, 0.3 mmol) and N-iodosuccinimide (NIS)
respectively. After mixing for a few seconds, UV–vis and fluorescence
5

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Compound 6 (0.7 mg, 0.001 mmol) was dissolved in 100 mL MeOH
to form 1 × 10ꢀ 5 mol/L solution. ZnCl2 (13.6 mg), CdCl2 (18.3 mg), Pd
(OAc)2 (22.4 mg), FeCl3 (16.2 mg), MnCl2⋅4H2O (19.8 mg), MgCl2⋅6H2O
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NiCl2⋅6H2O (23.8 mg), CuCl2⋅2H2O (17.0 mg), Cr (OAc)3 (22.9 mg),
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MeOH to form 0.01 mol/L solution, respectively. Then 30 μL (10 equiv.)
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10ꢀ 5 mol/L). After mixing for a few seconds, UV–Vis and fluorescence
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Furthermore, 30
μ
L (10 equiv) of 0.01 mol/L Cu2+ or Ni2+ solution was
firstly added into 3 mL 1 × 10ꢀ 5 mol/L probe 6 solution. Then the other
ions were added into the solution above. After mixing for a few seconds,
fluorescence spectra were taken at room temperature to measure the
competition with other metal ions.
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4.5. Calculation of detection limit
The detection limit was calculated by 3
σ
/K. Ten times of fluores-
cence intensity of compound 6 was test and
σ could be calculated. The
fluorescence intensity data were obtained according to the fluorescence
titrating for Cu2+ and Ni2+ (Excitation was provided at 542 nm and
emission intensity was measured at 589 nm). The linear regression curve
of probe 6 was then fitted to these fluorescence intensity data to
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Declaration of Competing Interest
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Acknowledgements
This work was the National Natural Science Foundation of China
(21301092), the Natural Science Foundation of Jiangsu province
(BK20151513), the Research Fund for the Doctoral Program of Higher
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