A novel ratiometric AIEE/ESIPT probe for palladium species detection with ultra-sensitivity

Article abstract of DOI:10.1039/c9ra06046d

Existing fluorescent probes for palladium (Pd) species detection have revealed their vulnerabilities, such as low sensitivity, poor anti-interference ability and long reaction time. In order to develop a faster and more accurate detection method for palladium species at extremely low concentrations, in this study, we designed a novel ratiometric AIEE/ESIPT probe (HPNI-1) based on the Tsuji-Trost reaction for Pd. According to the data obtained, the probe was able to detect Pd species with an ultra-high anti-interference ability (Pd : other metals = 1 : 1000), rapid detection time (within 2 minute) and ratiometric fluorescent signal changes with a 1.34 nM detection limit. This study not only proves that existing methods can be improved but also provides future prospects for HPNI-1 as one of the greatest probes for Pd species detection.

Full text of DOI:10.1039/c9ra06046d

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A novel ratiometric AIEE/ESIPT probe for palladium
species detection with ultra-sensitivity†
Cite this: RSC Adv., 2019, 9, 27937
a
a
Mingshu Zhang,a Rui Zhang,a Shudi Liub and Ying Yang
*
Zixuan Xu,
Existing fluorescent probes for palladium (Pd) species detection have revealed their vulnerabilities, such as
low sensitivity, poor anti-interference ability and long reaction time. In order to develop a faster and more
accurate detection method for palladium species at extremely low concentrations, in this study, we
designed a novel ratiometric AIEE/ESIPT probe (HPNI-1) based on the Tsuji–Trost reaction for Pd.
According to the data obtained, the probe was able to detect Pd species with an ultra-high anti-
interference ability (Pd : other metals ¼ 1 : 1000), rapid detection time (within 2 minute) and ratiometric
fluorescent signal changes with a 1.34 nM detection limit. This study not only proves that existing
methods can be improved but also provides future prospects for HPNI-1 as one of the greatest probes
for Pd species detection.
Received 4th August 2019
Accepted 22nd August 2019
DOI: 10.1039/c9ra06046d
rsc.li/rsc-advances
mechanisms. However, the majority of the coordination
mechanism-based probes show poor anti-interference ability
relative to other transition metal ions.12 On the contrary,
1. Introduction
Palladium (Pd) plays a crucial role in various elds, such as
functional materials, electric equipment, automobile exhaust
catalysts, jewelry, and chemical transformations.1–5 However,
due to limited Pd resources and extractive technologies, the
supply is not able to meet the demand, causing difficulties in
actual applications. Moreover, the environmental pollution
caused by the frequent use of Pd hinders the aim of sustainable
development. Moreover, according to some meaningful studies,
easily forming complexes between Pd and some bio-
macromolecules, such as proteins, DNA and RNA, have the
possibility of causing serious health problems.6,7 The European
Agency for the Evaluation of Medicinal Products (EMEA) sug-
gested that the threshold for residual Pd is 5–10 ppm.8 Hence, it
is critical to develop efficient methods for detecting Pd species.
Traditional detection methods for palladium species,
include X-ray uorescence, atomic absorption spectrometry
(AAS), and solid phase microextraction-high performance liquid
chromatography.9,10 However, these methods require expensive
instruments and high-level technicians. Recently, uorescence
detection for Pd has been a focal area owing to its high sensi-
tivity, high selectivity, simple operation and cost-effectiveness.11
Currently, uorescent probes for palladium species
detection are mainly based on coordination and catalytic
probes based on a catalytic mechanism usually show superior
selectivity.13–20 However, we noticed that some limitations
still exist in the detection of palladium based on catalytic
mechanism, such as long detection times and detection
difficulty in extremely low concentrations.21–25 In addition,
most uorophores of uorescence probes exhibit relatively
small Stokes shis, which hinders their applications in
quantitative determination due to self-absorption.18,26–28
Moreover, many probes detect OFF–ON or ON–OFF signal
output changes in their uorescence intensity. This type of
probe with a single uorescence change could be signi-
cantly inuenced by environmental effects, along with
a decrease in signal delity.24,29,30 Therefore, we urgently need
to develop a palladium uorescent probe that can overcome
the difficulties described above.31,32
Thus, we present a novel ratiometric probe HPNI-1 for
palladium species based on aggregated induced enhanced
emission (AIEE) and excited-state intramolecular proton trans-
fer (ESIPT) mechanisms (Fig. S2 and S3†). We specically
selected HPNI as the AIEE uorophore, and the terminal allyl
chloroformate was used as the recognition site and was modi-
ed on the hydroxyl group of HPNI to block the ESIPT process.33
Aer palladium treatment, the ESIPT process was recovered
under ultraviolet excitation, resulting in tautomerization and
a large Stokes shi (240 nm) (shown in Schemes 2 and 3).
Moreover, we were able to get a meaningful data that showed
that HPNI-1 had an ultra-fast reaction time and ultra-low
detection concentration for palladium detection. Thus, we
suggest that HPNI-1 is one of the best uorescent probes of
palladium species detection.
aLaboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu
Province, College of Chemistry and Chemical Engineering, Lanzhou University,
Lanzhou 730000, Gansu, P. R. China. E-mail: yangying@lzu.edu.cn
bCollege of Chemistry and Chemical Engineering, Yantai University, Yantai, 264005, P.
R. China
† Electronic supplementary information (ESI) available: Materials and methods,
synthesis, the characterization data of HPNI-1 and additional spectra. See DOI:
10.1039/c9ra06046d
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Scheme 1 Synthesis of HPNI-1.
69.18. ESI-MS: calcd for [C35H26N2O3 + H+], 523.2016; found,
523.2028.
2. Material and methods
2.1 Materials and instruments
All reagents and solvents were obtained commercially and used
without further purication unless otherwise noted. 1H NMR
and 13C NMR spectra were recorded on a JEOLBCS 400M spec-
trometer. Mass spectra (ESI) were recorded on a LQC system
(Finnigan MAT, USA). All UV-visible spectra were recorded on
a Varian Cary 100 spectrophotometer. Fluorescence spectra
were recorded using an Edinburgh FLSP920. Fluorescence
spectra were recorded aer the addition of palladium for 1 min.
2.3 General procedure for spectral measurements
HPNI-1 (1 mM) was dissolved in THF and maintained at room
temperature. Stock solutions of Pd(PPh3)4, Pd(PPh3)2Cl2,
Pd2(dba)3, and (C3H5)2PdCl2 (0.1 mM) were prepared in DMSO
as the sources of Pd and used freshly. Zn2+, Ni2+, Na2+, Mn2+, K+,
Cr3+, Co2+, Cd2+, Ca2+, Ba2+, NO3ꢁ, Clꢁ, SO42ꢁ, CO32ꢁ, AcOꢁ,
SCN, and Iꢁ (10 mM) were prepared in deionized water by dis-
solving the corresponding salts. Test solutions were prepared by
placing 20 mL of HPNI-1 stock solution into a quartz cell,
diluting the solution to 2 mL with an acetonitrile-and-water
mixed solution (CH3CN : H2O ¼ 3 : 2, KBH4 ¼ 1 mM), and
then different analytes were added. All of the UV-vis absorption
and uorescence measurements were taken at room tempera-
ture. The selected excitation and emission wavelengths were at
2.2 Synthesis of HPNI and HPNI-1
Precursor HPNI was prepared according to the following
procedures.9
To a solution of HPNI (200 mg, 0.456 mmol) and allyl
chloroformate (0.5 mL) in THF (20 mL), was added triethyl-
amine (0.15 mL, 1 mmol) dropwise at 0 ꢀC for 30 min. Aer that,
the mixture was stirred at room temperature for 2 h. Then, the
mixture was extracted with dichloromethane, and the combined
organic phase was dried over anhydrous Na2SO4. The solvent
was removed under reduced pressure, and the residue was
puried via column chromatography on silica gel with a mixture
of ethyl acetate/petroleum ether (1 : 4, v/v) as the eluent to
1
obtain HPNI-1 as a yellow solid (0.21 g, 90.3%). H NMR (400
MHz, CDCl3) d 7.69 (d, J ¼ 8.1 Hz, 1H), 7.65 (s, 1H), 7.60 (s, 1H),
7.53 (d, J ¼ 7.1 Hz, 3H), 7.37 (ddd, J ¼ 29.2, 11.0, 4.0 Hz, 2H),
7.23–7.14 (m, 5H), 7.14–7.03 (m, 6H), 6.98 (dd, J ¼ 8.0, 1.5 Hz,
2H), 5.73 (ddt, J ¼ 16.3, 10.5, 5.8 Hz, 1H), 5.12 (ddd, J ¼ 13.8,
11.5, 1.2 Hz, 2H), 4.52 (d, J ¼ 5.8 Hz, 2H). 13C NMR (101 MHz,
CDCl3) d 153.04, 146.72, 142.94, 138.46, 136.63, 134.43, 133.49,
132.19, 131.18, 131.13, 130.82, 130.67, 130.51, 128.81, 128.42,
Fig. 1 Emission spectra of HPNI in different solutions. Concentration
128.08, 128.00, 127.43, 127.30, 126.59, 126.19, 119.56, 119.21, 10 mM, lex ¼ 365 nm.
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Scheme 2 The sensing mechanism of HPNI-1 for the selective recognition of palladium.
365 nm and 570 nm, respectively. The excitation slit width was
3. Results and discussion
5 nm, and emission slit width was 5 nm. The uorescence
spectra were recorded aer 2 min aer the addition of analytes
into the quartz cell to allow the complete mixing of the analytes
into the solution.
The synthetic process of the probe HPNI-1 is shown in Scheme
1. We chose HPNI as the uorophore due to its large Stokes shi
(240 nm) by the excited-state intramolecular proton transfer
(ESIPT) process. This uorophore also has a high uorescence
quantum yield (F ¼ 0.22). Terminal allyl chloroformate was
used as the recognition site, which was modied on the
hydroxyl group of HPNI to block the ESIPT process. HPNI-1 was
2.4 Determination of the detection limit
According to the uorescence titration, the uorescence inten-
sity ratio (I570/I410) and the concentration of Pd(0) (0–50 nM)
showed an excellent linear relationship. The detection limit was
calculated by the following equation:
1
characterized by H NMR, 13C NMR and HR-MS.
3.1 The uorescence spectrum of HPNI in various solutions
The emission spectra of HPNI in different solutions are shown
in Fig. 1. We noticed that HPNI has dual emission bands, which
Detection limit ¼ 3s/k
(1)
where s is the standard deviation of the blank sample can be attributed to the coexistence of two tautomers in the
(measured 10 times) and k is the slope of the linear regression ESIPT process (Scheme 3). We suggest that the shorter emission
equation.
bands are ascribed to the enol form of HPNI. Relatively, the
Scheme 3 General mechanism of ESIPT process and chemical structures of enol form (E) and keto from (K) in the ESIPT process of HPNI.
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Fig. 2 (a) Fluorescence spectral changes of HPNI-1 (10 mM) and (b) the relationship between fluorescence intensity and reaction time upon
treatment with Pd(PPh3)4 (2 mM) in acetonitrile–water solution (CH3CN : H2O ¼ 3 : 2, KBH4 (1 mmol)) Ex ¼ 365 nm.
longer emission band can be assigned to the keto form of HPNI. a new emission band appeared at 570 nm, which created an
HPNI exhibits strong uorescence emission at 570 nm and isosbestic point at 460 nm that exhibited a ratiometric
extremely weak uorescence emission at 410 nm in acetonitrile, response. The large red-shi (160 nm) is due to the ESIPT
indicating that the keto form is the main form of HPNI in process being recovered. Notably, the uorescence intensity
acetonitrile. Therefore, choosing acetonitrile as the solvent reached equilibrium within 2 min.
makes detection more reliable. In addition, in the mixed solu-
tion of CH3CN and H2O at various ratios, HPNI and HPNI-1 had
3.3 The sensitivity
relatively high uorescence intensities when CH3CN : H2O ¼
3 : 2 (Fig. S1 and S2†). Therefore, we chose CH3CN : H2O ¼ 3 : 2
Fig. 3a shows the uorescence changes with various amounts of
Pd(PPh3)4 in a CH3CN : H2O (3 : 2 v/v) solution with KBH4 (1
mixed solutions as a solvent.
mM) aer 2 min. When the concentration of Pd(PPh3)4 gradu-
ally increases, the uorescence peak at l ¼ 410 nm shows a slow
3.2 Fluorescence response toward Pd(0)
decrease, and a new uorescence peak appears at l ¼ 570 nm
The uorescence spectra of HPNI-1 (CH3CN : H2O ¼ 3 : 2, and then becomes the maximum peak. The ratio of the uo-
KBH4: 1 mmol) at room temperature was investigated (Fig. 2), rescence intensities (l570/l410) changes from 0.18 to 5.34 (R ¼
and HPNI-1 showed uorescence emission at 410 nm upon 30.24-fold). More importantly, as the concentration of
excitation at 365 nm. Aer reaction with palladium, a decrease Pd(PPh3)4 increases from 0 to 500 nM, the ratio of the uores-
in the emission intensity at 410 nm was observed. Moreover, cent intensity shows an excellent linear relationship.
Fig. 3 (a) Fluorescent spectral changes of HPNI-1 (10 mM) upon addition of different concentrations of Pd(PPh3)4 (0–1 mM) in acetonitrile–water
solutions (CH3CN : H2O ¼ 3 : 2, KBH4: 1 mM) at room temperature. Each spectrum was obtained 2 min after Pd(PPh3)4 addition. Ex ¼ 365 nm.
Slit: 5.0 nm/5.0 nm. Inset: The fluorescent intensity ratio changes at 570 and 410 nm (I570/I410) against the concentrations of Pd(PPh3)4. (b) Linear
relationship of the I570/I410 as a function of the concentration of Pd(PPh3)4 from 5 to 50 nM.
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Fig. 4 (a) Fluorescent spectral (b) fluorescence intensity and (c) photograph of HPNI-1 (10 mM) with the addition of Pd(PPh3)4 (1 mM) and other
metal ions (1 mM) in acetonitrile–water solutions (CH3CN : H2O ¼ 3 : 2, KBH4: 1 mM) at room temperature. Each spectrum was obtained 2 min
after the metal ion addition. Ex ¼ 365 nm. Slit: 5.0 nm/5.0 nm.
The ratiometric uorescent detection method is based on HPNI-1 can serve as a sensitive ratiometric uorescent sensor
the ratio of the two uorescent bands rather than the absolute for the quantitative detection of Pd.
emission intensity of one band, making it possible to analyze
palladium species more accurately and sensitively by mini-
mizing the background signal. Moreover, under the ultra-low
3.4 The sensitivity
Selectivity experiments were performed with different metal
ions (Fig. 4). In the mixed solution (CH3CN : H2O ¼ 3 : 2, KBH4
¼ 1 mM), the ratiometric response can only be detected when
concentrations of Pd(PPh3)4, the good linear relationship is
maintained (Fig. 3b). According to the data presented in the
research and eqn (1), the detection limit of HPNI-1 for Pd(0) is
1.34 nM. (The sensitivity of HPNI-1 was far beyond those of
other reported studies and much lower than the palladium
content in the samples of human saliva (7.4 mg Lꢁ1)). That is,
Pd(0) (1 mM) is added to the solution. Other metals such as Zn2+
,
Ni2+, Na2+, Mn2+, K+, Cr3+, Co2+, Cd2+, Ca2+ and Ba2+ (1 mM) have
no or an insignicant inuence on the detection. Under UV
light (365 nm), signicant orange uorescence is observed. The
Fig. 5 (a) Fluorescence spectra and (b) fluorescence intensity of HPNI-1 (10 mM) with the addition of Pd(PPh3)4 (1 mM) and other anions (1 mM) in
acetonitrile–water solutions (CH3CN : H2O ¼ 3 : 2, KBH4: 1 mM) at room temperature. Each spectrum was obtained 2 min after metal ion
addition. Ex ¼ 365 nm. Slit: 5.0 nm/5.0 nm.
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Fig. 6 (a) Fluorescence detection and (b) fluorescence intensity ratio (I570/I410) of Pd(PPh3)4 (0.3 mM) with HPNI-1 (10 mM) in the presence of other
metal ions (0.3 mM) in acetonitrile–water solutions (CH3CN : H2O ¼ 3 : 2, KBH4: 1 mM) at room temperature. Each spectrum was obtained 2 min
after metal ion addition. Ex ¼ 365 nm. Slit: 5.0 nm/5.0 nm.
experimental results of the interference of the above-mentioned
metal ions on Pd(0) show that HPNI-1 possesses ultra-high
selectivity for palladium detection. ([Pd(0)]/[Mn+] ¼ 1 : 1000).
Similarly, we conducted selectivity and anti-interference
experiments on the anions (NO3ꢁ, Clꢁ, SO42ꢁ, CO32ꢁ, AcOꢁ,
SCN, and Iꢁ) (Fig. 5), and HPNI-1 again showed excellent
selectivity for the palladium species.
3.6 The sensing behavior of HPNI-1 for other palladium
sources
To verify the potential application of HPNI-1, we tested whether
the probe could detect all the oxidation states of Pd
[Pd(0) : Pd(PPh3)4,
Pd2(dba)3;
Pd(II) : PdCl2(PPh3)2,
(C3H5)2PdCl2; Pd(IV) : K2PdCl6]. According to the intensity ratio
(I570/I410), the sensitivity of HPNI-1 to palladium was PdCl2(-
PPh3)2 > Pd(PPh3)4 > Pd2(dba)3 > (C3H5)2PdCl2 > K2PdCl6, as
shown in Fig. 7. The results showed that HPNI-1 has a signi-
cant response to all the oxidation states of palladium, and the
uorescence changed signicantly. In addition, we noticed that
in the detection of palladium complexes, containing organic
ligands had relatively stronger uorescence intensities.
3.5 The anti-interference ability
We also investigated the anti-interference ability of HPNI-1; as
shown in Fig. 6, we can observe the uorescence responses for
Pd(0) detection at high concentrations of the metal ion solu-
tions (metal ions : Pd(PPh3)4 ¼ 1000 : 1). Due to its ultra-high
anti-interference characteristic, HPNI-1 possesses a great prac-
tical application value for Pd(0) detection.
To deeply investigate the reaction mechanism of HPNI-1 and
Pd(PPh3)4, 1H NMR titration experiment was performed in
Fig. 7 The fluorescence responses of HPNI-1 (10 mM) to various palladium sources (1 mM). (CH3CN : H2O ¼ 3 : 2, KBH4: 1 mM).
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Fig. 8 Stacked 1H NMR spectra of (a) HPNI-1 and (b) upon addition of Pd(PPh3)4 in DMSO-d6.
DMSO-d6 (Fig. 8). For HPNI-1, the multiple peaks between 5.75
Acknowledgements
and 5.93 ppm and the doublet peaks appearing at 5.28 and
5.15 ppm were assigned to the CH] and ]CH2 protons in the
allyl group, respectively (Fig. 8a). These characteristic peaks
disappeared in the 1H NMR spectrum aer Pd(PPh3)4, treat-
ment (0.1 equiv.) (Fig. 8b). Moreover, a new peak attributed to
the OH group in HPNI appeared at 12.03 ppm. It is clear that the
1H NMR spectrum is almost identical to that of standard
HPNI,33 demonstrating that the reaction of HPNI-1 with Pd0
results in the release of HPNI–OH. Based on these results and
some previous reports, the mechanism of HPNI-1 for Pd0
detection is illustrated in Scheme 2.
This work was supported by the National Natural Science
Foundation of China (Grant 51474118, 21701074).
References
1 SESSION, DWHORATR International Programme on
Chemical Safety, 2009.
2 R. Martin and S. L. Buchwald, Acc. Chem. Res., 2008, 41,
1461–1473.
3 W. Wu and H. Jiang, Acc. Chem. Res., 2012, 45, 1736–1748.
4 S.-Y. Ding, J. Gao, Q. Wang, Y. Zhang, W.-G. Song, C.-Y. Su
and W. Wang, J. Am. Chem. Soc., 2011, 133, 19816–19822.
5 Z. He, B. Dong, W. Wang, G. Yang, Y. Cao, H. Wang, Y. Yang,
Q. Wang, F. Peng and H. Yu, ACS Catal., 2019, 9, 2893–2901.
6 J. Wataha and C. Hanks, J. Oral Rehabil., 1996, 23, 309–320.
7 J. Kielhorn, C. Melber, D. Keller and I. Mangelsdorf, Int. J.
Hyg. Environ. Health, 2002, 205, 417–432.
8 C. E. Garrett and K. Prasad, Adv. Synth. Catal., 2004, 346,
889–900.
9 K. Van Meel, A. Smekens, M. Behets, P. Kazandjian and
R. Van Grieken, Anal. Chem., 2007, 79, 6383–6389.
10 C. Locatelli, D. Melucci and G. Torsi, Anal. Bioanal. Chem.,
2005, 382, 1567–1573.
4. Conclusion
In conclusion, we successfully synthesized a novel uorescence
probe (HPNI-1) for palladium species detection based on
a Pd(0)-triggered cleavage reaction. HPNI-1 possessed ultra-high
selectivity and anti-interference ability. Moreover, HPNI-1
exhibited obvious ratiometric uorescence responses toward
palladium due to the ESIPT process, with a color change from
weak blue to strong orange. Moreover, the probe had an
astonishing detection limit (1.34 nM), which has far exceeds
those of other reported probes. Thus, we suggest that HPNI-1
has great potential to detect ultra-low concentrations of palla-
dium species in environmental settings.
11 H. Li, J. Fan and X. Peng, Chem. Soc. Rev., 2013, 42, 7943–
7962.
12 M. N. Yara¸sir, M. Kandaz, A. Koca and B. Salih, Polyhedron,
2007, 26, 1139–1147.
13 J. Jiang, H. Jiang, W. Liu, X. Tang, X. Zhou, W. Liu and R. Liu,
Org. Lett., 2011, 13, 4922–4925.
Conflicts of interest
The authors declare no competing nancial interest.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 27937–27944 | 27943

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Paper
14 M. Santra, S.-K. Ko, I. Shin and K. H. Ahn, Chem. Commun., 24 J.-w. Yan, X.-l. Wang, Q.-f. Tan, P.-f. Yao, J.-h. Tan and
2010, 46, 3964–3966. L. Zhang, Analyst, 2016, 141, 2376–2379.
15 B. Liu, H. Wang, T. Wang, Y. Bao, F. Du, J. Tian, Q. Li and 25 T. Gao, P. Xu, M. Liu, A. Bi, P. Hu, B. Ye, W. Wang and
R. Bai, Chem. Commun., 2012, 48, 2867–2869. W. Zeng, Chem.–Asian J., 2015, 10, 1142–1145.
16 R. M. Yusop, A. Unciti-Broceta, E. M. Johansson, 26 X. Teng, M. Tian, J. Zhang, L. Tang and J. Xin, Tetrahedron
´
´
R. M. Sanchez-Martın and M. Bradley, Nat. Chem., 2011, 3,
Lett., 2018, 59, 2804–2808.
239.
27 H. Nie, J. Geng, J. Jing, Y. Li, W. Yang and X. Zhang, RSC Adv.,
2015, 5, 97121–97126.
28 W. Luo and W. Liu, Dalton Trans., 2016, 45, 11682–11687.
17 Q. Xia, S. Feng, D. Liu and G. Feng, Sens. Actuators, B, 2018,
258, 98–104.
18 W. Feng, L. Bai, S. Jia and G. Feng, Sens. Actuators, B, 2018, 29 M. Liu, T. Leng, K. Wang, Y. Shen and C. Wang, J. Photochem.
260, 554–562. Photobiol., A, 2017, 337, 25–32.
19 X. Jie, M. Liu, A. Peng, J. Huang, Y. Zhang, X. Wang and 30 W. Su, B. Gu, X. Hu, X. Duan, Y. Zhang, H. Li and S. Yao, Dyes
Z. Tian, Talanta, 2018, 183, 164–171. Pigm., 2017, 137, 293–298.
20 J. Zhou, S. Xu, Z. Yu, X. Ye, X. Dong and W. Zhao, Dyes Pigm., 31 L. Zhou, Q. Wang, X.-B. Zhang and W. Tan, Anal. Chem.,
2019, 170, 107656. 2015, 87, 4503–4507.
21 W. Luo, J. Li and W. Liu, Org. Biomol. Chem., 2017, 15, 5846– 32 L. Zhou, S. Hu, H. Wang, H. Sun and X. Zhang, Spectrochim.
5850. Acta, Part A, 2016, 166, 25–30.
22 B. Zhu, C. Gao, Y. Zhao, C. Liu, Y. Li, Q. Wei, Z. Ma, B. Du and 33 S. Park, J. E. Kwon, S. H. Kim, J. Seo, K. Chung, S.-Y. Park,
X. Zhang, Chem. Commun., 2011, 47, 8656–8658.
23 H. Chen, W. Lin and L. Yuan, Org. Biomol. Chem., 2013, 11,
1938–1941.
D.-J. Jang, B. M. Medina, J. Gierschner and S. Y. Park, J.
Am. Chem. Soc., 2009, 131, 14043–14049.
27944 | RSC Adv., 2019, 9, 27937–27944
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