A novel rhodamine B and purine derivative-based fluorescent chemosensor for detection of palladium (II) ion

Article abstract of DOI:10.1016/j.inoche.2019.02.038

A new rhodamine B and purine-based colorimetric and fluorescent sensor RBTP for detection of Pd (II) cation was prepared and structurally characterized. Sensor RBTP shows high sensitivity and selectivity to Pd²⁺ in EtOH/H₂O solution (3/2, v/v, pH 7.4, HEPES buffer, 0.5 mM). And sensor RBTP not only exhibited a naked-eye color change from colorless to pink, but also displayed “turn-on” fluorescent sensing for recognition and detection of Pd²⁺. The fluorescence titration analysis of sensor RBTP to Pd²⁺ exhibits a low the limit of detection (49.5 nM). A great linear relationship was found between the concentration of Pd²⁺ from 0 to 40 μM and the fluorescence intensity of RBTP. The crystal structure of RBTP was supported by X-ray diffraction. Meanwhile, the proposed sensing mechanism of RBTP binding to Pd²⁺ was supported by Job's plot, MS spectra study and density functional theory (DFT) study. Moreover, sensor RBTP could be made as test paper to quantitative detection for Pd (II) cation in water.

Full text of DOI:10.1016/j.inoche.2019.02.038

Accepted Manuscript
A novel rhodamine B and purine derivative-based fluorescent
chemosensor for detection of palladium (II) ion
Guowei Wu, Zhengyi Wang, Weixia Zhang, Wei Chen, Xinxin
Jin, Hongfei Lu
PII:
S1387-7003(19)30088-7
DOI:
Reference:
https://doi.org/10.1016/j.inoche.2019.02.038
INOCHE 7296
To appear in:
Inorganic Chemistry Communications
Received date:
Revised date:
Accepted date:
23 January 2019
22 February 2019
24 February 2019
Please cite this article as: G. Wu, Z. Wang, W. Zhang, et al., A novel rhodamine B
and purine derivative-based fluorescent chemosensor for detection of palladium (II) ion,
Inorganic Chemistry Communications, https://doi.org/10.1016/j.inoche.2019.02.038
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ACCEPTED MANUSCRIPT
A novel rhodamine B and purine derivative-based fluorescent
chemosensor for detection of palladium (II) ion
§
§
Guowei Wua , Zhengyi Wanga , Weixia Zhanga, Wei Chena, Xinxin Jina, Hongfei
Lua*
aSchool of Environmental and Chemical Engineering, Jiangsu University of Science
and Technology, 212003 Zhenjiang, China.
E-mail: zjluhf1979@just.edu.cn
ABSTRACT
A new rhodamine B and purine-based colorimetric and fluorescent sensor RBTP
for detection of Pd (II) cation was prepared and structurally characterized. Sensor
RBTP shows high sensitivity and selectivity to Pd2+ in EtOH/H2O solution (3/2, v/v,
pH 7.4, HEPES buffer, 0.5 mM). And sensor RBTP not only exhibited a naked-eye
color change from colorless to pink, but also displayed “turn-on” fluorescent sensing
for recognition and detection of Pd2+. The fluorescence titration analysis of sensor
RBTP to Pd2+ exhibits a low the limit of detection (49.5 nM). A great linear
relationship was found between the concentration of Pd2+ from 0 to 40 μM and the
fluorescence intensity of RBTP. The crystal structure of RBTP was supported by
X-ray diffraction. Meanwhile, the proposed sensing mechanism of RBTP binding to
Pd2+ was supported by Job’s plot, MS spectra study and density functional theory
(DFT) study. Moreover, sensor RBTP could be made as test paper to quantitative
detection for Pd (II) cation in water.
Key words: Fluorescent sensor; Purine; Rhodamine B; Palladium
1. Introduction
Palladium, one of the platinum group elements, plays a vital role in numerous
fields including catalytic converters, electronics, medical instruments, dentistry, fuel
cells, groundwater and jewelry [1-5]. In drug synthesis and related fields, palladium
could remain as an impurity in the final product due to its frequent use, which is
harmful to human health [6-7]. DNA, proteins and other biomacromolecules can form
complexes with palladium, which may lead to a variety of cellular dysfunction
progress [8-12]. According to European Agency for the Evaluation of Medicinal
Products, the threshold limit of Palladium found in drugs should be less than 5-10
ppm and the proposed dietary intake of Palladium as 1.5-15 mg per person per day

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[13-14]. Therefore, considerable effort has been focused on monitoring Palladium,
and the development of effective methods for the detection of presence of palladium
species is highly desirable.
Conventional methods of palladium detection have been established mainly
including atomic absorption spectrometry, inductively coupled plasma atomic
emission spectrometry, solid phase micro extraction-high performance liquid
chromatography, inductively coupled plasma mass spectrometry [15-18]. However, all
these methods have some shortcomings such as complex progress, rigorous
experimental conditions, high consumption of time and high cost [19-22]. Compared
with these methods, fluorescent technique could avoid the disadvantages, owing to
instance simple operation, fast response, low cost, simple progress and ‘naked eye’
[23-28].
A series probes have been demonstrated for the detection of palladium. The probes
for detection of palladium are mainly based on chromen [29], rhodamine dyes [30-33],
benzothiazole [31], cynines [34], naphtalimide [35], and fluorescein [36]. Despite the
success of these probes, the development of probes for palladium still remains a
challenging task because of long response time, harsh pH condition and high
detection limit [37-39]. Therefore, there is still a strong demand for the design of new
probes.
Biological compatibility is an important and advantageous condition for an
excellent fluorescence sensor. Purine nucleosides are ubiquitous in RNA and DNA
and have distinguished biocompatibility. They are parts of many molecules of
biological importance and thus provide an excellent scaffold for the construction of
bioprobes [40-42]. Owing to various biological activities and significant application
value, Purine derivatives are also widely used as important antiviral drug
intermediates.
Rhodamine fluorophore has a special photoluminescent property, its spirolactam
form (which is colorless and non-fluorescent) and the ring-opened form (which is
pink and strongly fluorescent) would be triggered by a specific analyte [43-45].
Herein, we report a new fluorescent palladium probe (RBTP) obtained by combining
rhodamine with purine derivative into a framework (scheme 1) for the detection of
palladium in EtOH/H2O (3:2 v/v) buffered with HEPES (pH= 7.4). And sensor RBTP
shows high sensitivity and selectivity to Pd2+, with detection limit reaching 49.5 nM.

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Scheme 1. Synthesis of RBTP
2. Experimental
2.1. Reagents
Unless otherwise statement, all chemical reagents and solvents were of analytical
grade. Rhodamine B, ethanediamine, 1-Naphthalenamine, 5-Amino-4, 6-dichoropyri-
midine, PPA, acetic acid and phosphorus oxychloride were purchased from Energy
Chemical, and used without further purification. Water used throughout all experim-
ents was twice-distilled. All solvents and metal ions AgNO3, CdCl2, Cs2CO3, FeCl3,
MgCl2·6H2O, HgCl2, ZnCl2, CaCl2, PdCl2, PtCl2, BaCl2·2H2O, NaCl, KCl, AlCl3,
CuCl2·2H2O, CoCl2·6H2O, Pb(NO3)2, NiCl2·6H2O, MnCl2 were purchased from
shanghai Wohua Chemical Co., Ltd..
2.2. General instrumentations
1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were measured on Bruker
-Advance DPX 400 spectrometer by using DMSO and CDCl3 as solvents and tetra-
methylsilane (TMS) as the internal reference. The chemical shifts were acquired in
parts-per-million (ppm). Mass spectra were carried out from mass spectrometer
(Agilent-6110). Fluorescent spectra were performed on Spectrofluorometer FS5.
UV-vis spectra were acquired by U3010-vis spectrophotometer. Quartz cuvettes were
used for throughout all measurements with a 1-cm path length and 3-mL volume. All
measurements were made in quartz cubes with a length of 1 cm and a volume of 3 mL.
The pH levels were obtained with FE20. Thin-layer chromatography (TLC) was
performed with Haiyang silica gel F 254 plate and column chromatography was cond-
ucted over Haiyang silica gel (type: 200-300 mesh, 300-400 mesh).
2.3. Synthesis
The intermediate compounds 1-3 were synthesized according to the reported proc-
edure [46-47].

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2.3.1. Synthesis of compound 1
Rhodamine B (2 g, 4.499 mmol) was added into 30 mL of anhydrous ethanol and
was heated for 20 minutes, and ethanediamine (3.0 mL, 44.98 mmol) was added. The
mixture was stirred at 80 ℃ for 12 hours. After the complete consumption of the
starting material monitored using TLC, the mixture was cooled to room temperature.
Then the mixture was evaporated in reduced pressure, and the residue was dissolved
in distilled water. Next the mixture was extracted with dichloromethane three times,
and the organic phase was washed with saturated saline, and dried with anhydrous
sodium sulfate. After filtered, the solvent was removed under reduced pressure and
crude product was obtained. The crude product was purified by silica gel
chromatography using MeOH/DCM (v/v, 1/50) to produce compound 1 as light
1
yellow powder (1.81 g, yield 83 %). H NMR (CDCl3, 400 MHz) δ 7.97 – 7.87 (m,
1H), 7.51 – 7.44 (m, 2H), 7.16 – 7.07 (m, 1H), 6.45 (d, J = 8.8 Hz, 2H), 6.39 (d, J =
2.6 Hz, 2H), 6.29 (dd, J = 8.9, 2.6 Hz, 2H), 3.35 (q, J = 7.1 Hz, 8H), 3.21 (t, J = 6.6
Hz, 2H), 2.45 (t, J = 6.6 Hz, 2H), 1.65 (s, 2H), 1.18 (t, J = 7.0 Hz, 12H). ESI-MS:
calcd. for [M+H]+ 485.28; found, 485.3.
2.3.2. Synthesis of compound 2
In a 100 mL round bottom flask, 5-Amino-4, 6-dichloropyrimidine (5.00 g, 30
mmol) and 1-Naphthylamine (8.584 g, 60 mmol) were added and were dissolved in
methanol (50 mL), then HCl (5 mL, 60 mmol) were added. The mixture was stirred at
65 ℃ for 24 h. After cooling, the solvent was evaporated under reduced pressure.
Then 1 N NaOH was added to the residue and the mixture was extracted with ethyl
acetate three times. The organic phase was washed with 1.2 N HCl and saturated
saline, and evaporated to obtain the crude produce. The crude product was recry-
stallized with CH3OH/H2O (v/v, 1:5) to product the compound 2 as a pale violet
1
powder (5.751 g, yield 71 %). H NMR (400 MHz, DMSO-d 6 ) δ 8.79 (s, 1H), 8.00 –
7.94 (m,1H), 7.89 (ddd, J = 7.4, 2.2, 0.9 Hz, 1H), 7.86 – 7.81 (m, 1H), 7.64 (s, 1H),
7.56 (d, J= 2.2 Hz, 1H), 7.54 (d, J = 2.6 Hz, 1H), 7.53 (t, J = 2.3 Hz, 1H), 5.76 (s, 1H),
5.47 (s,2H). ESI-MS: calcd. for [M+H]+ 271.07, found 271.1. Mp 173.8-175.1.
2.3.3. Synthesis of compound 3
Compound 2 (5 g, 18.5 mmol), acetic acid (5.882 g, 98 mmol), and DTAC (0.448
g, 10 %mmol) were dissolved in 60 mL of POCl3, then PPA (25 g, 74 mmol) was
added. The reaction mixture was stirred overnight at 80 ℃. After the reaction was
completed, the mixture was cooled to room temperature, the solvent was evaporated
under reduced pressure and the brown oil was obtained. And ice water mixture was
added to the oil to get light yellow powder (2.535 g, yield 50 %). 1H NMR (400 MHz,
DMSO-d 6) δ 8.60 (s, 1H), 8.26 (dt, J =8.0, 1.1 Hz, 1H), 8.17 (d, J = 8.2 Hz, 1H), 7.83
– 7.73 (m, 2H), 7.66 (ddd, J = 8.2, 6.9, 1.2 Hz, 1H), 7.52 (ddd, J = 8.3, 6.9, 1.3 Hz,

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13
1H), 7.21 (dd, J = 8.5, 1.0 Hz, 1H), 2.38(s, 3H). C NMR (101 MHz, DMSO-d 6 ) δ
156.89, 151.31, 148.73, 145.94, 134.27, 130.78, 130.51, 130.10, 128.93, 128.38,
127.41, 127.19, 126.20, 123.55, 122.33, 14.11. ESI-MS: calcd. for [M+H]+ 295.07,
found 295.1. Mp, 223.6-224.7. Elementalanalysis (%): calcd. C 65.20, N 19.01, H
3.76; found, C 65.31, N 19.15, H 3.77.
2.3.4. Compound RBTP
Compound 1 (1.86 g, 4.08 mmol) and compound 3 (1 g, 3.4 mmol) were dissolved
in 40 mL of methanol, then Na2CO3 (1.3 g, 17 mmol) was added. And the reaction
mixture was allowed to stir 24 h at 80 ℃. After the reaction was completed, the
mixture was cooled to room temperature. The resulting solid is filtered and the solvent
was removed by vacuum rotary evaporation. The crude product was purified by
column chromatography on silica gel using CH3OH/CH2Cl2 (v/v, 1/150) to get light
1
yellow solid (1.21 g, yield: 48 %). H NMR (400 MHz, DMSO-d6) δ 8.18 (d, J = 8.1
Hz, 1H), 8.12 (d, J = 8.2 Hz, 1H), 7.90 (s, 1H), 7.85 – 7.81 (m, 1H), 7.71 (dd, J = 8.3,
7.3 Hz, 1H), 7.65 – 7.57 (m,3H), 7.55 – 7.45 (m, 3H), 7.08 – 6.98 (m, 2H) 6.42 – 6.34
(m, 6H), 3.30 (q, J = 7.0 Hz,10H), 2.19 (s, 3H), 1.24 (s, 1H), 1.06 (t, J = 7.0 Hz, 12H).
13C NMR (101 MHz, DMSO-d6) δ 167.94 , 154.20 , 153.98 , 153.22 , 152.44 ,
134.32 , 133.20 , 131.16 , 130.73 , 130.25, 128.81, 128.18 , 127.25, 126.23 , 124.10 ,
122.80 , 122.42 , 108.60 , 97.81 , 64.79 , 44.12 , 14.18 , 12.85. MS (ESI) m/z: calcd.
for [M+H]+ 743.37; found 743.3.
2.4. Stock solution
A stock solution of RBTP (1 mM) was prepared in EtOH/H2O (3/2, v/v, pH 7.4,
HEPES buffer, 0.5 mM). The stock solutions (3 mM) of chloride salts of Zn2+, Ni2+,
Pt2+, Fe3+, Na+, Mn2+, Al3+, Ca2+, Ba2+, Cu2+, K+, Cd2+, Mg2+, Co2+, Hg2+ and AgNO3,
CsCO3, Pb(NO3)2 were prepared in EtOH/H2O (3/2, v/v, pH 7.4, HEPES buffer, 0.5
mM).
2.5. General method of UV-vis and fluorescence
The UV-vis and fluorescent methods were performed in EtOH/H2O solution (3/2,
v/v, pH 7.4, HEPES buffer, 0.5 mM) to evaluate the nature of RBTP. The UV-vis
absorption spectra and fluorescent spectra were measured at room temperature.
Fluorescence spectra were obtained in a quartz cell with 562 nm excitation
wavelength and 584 nm emission wavelength.
3. Results and Discussion
3.1. X-ray Crystal Structure Studies of RBTP
The crystals which were suitable for X-ray diffraction study were obtained in the

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ethanol solution of RBTP at room temperature. The X-ray diffraction of the white
single crystal was conducted on the single crystal diffractometer. X-ray crystallo-
graphy structural study displayed RBTP crystallized in space group P -1 of the
triclinic system. As shown in Fig. 1, the novel fluorescence sensor RBTP exhibited in
a closed spironolactone ring structure.
Fig. 1. X-ray crystal structure of RBTP
3.2. UV-vis spectral response of sensor RBTP to Pd2+
The spectral response of sensor RBTP to Pd2+ was measured by the UV-vis
absorption spectrum in the EtOH/H2O solution (3/2, v/v, pH 7.4, HEPES buffer, 0.5
mM). As shown in Fig. 2, sensor RBTP (20 μM) displays a very weak absorption
band at 562 nm. Upon addition of Pd2+ (100 μM), a new band was observed at 562 nm,
while the other metal ions, including Zn2+, Ni2+, Pt2+, Fe3+, Na+, Mn2+, Al3+, Ca2+,
Ba2+, Cu2+, K+, Cd2+, Mg2+, Co2+, Hg2+ and AgNO3, CsCO3, Pb(NO3)2, did not
generate any change of UV-vis absorption spectra. Thus sensor RBTP has good
UV-vis absorption spectrum response toward Pd2+.
Fig. 2. UV-vis absorption spectra of sensor RBTP (20 μM) upon addition of Pd2+ (100 μM) and
various other metal ions (100 μM, respectively) in the EtOH/H2O solution (3/2, v/v, pH 7.4,
HEPES buffer, 0.5 mM)

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3.3. Selective response of sensor RBTP towards Pd2+
The selectivity of sensor RBTP towards Pd2+ was studied in EtOH/H2O solution
(3/2, v/v, pH 7.4, HEPES buffer, 0.5 mM). The chloride salts of Zn2+, Ni2+, Pt2+, Pd2+,
Fe3+, Na+, Mn2+, Al3+, Ca2+, Ba2+, Cu2+, K+, Cd2+, Mg2+, Co2+, Hg2+ and AgNO3,
CsCO3, Pb(NO3)2 (100 μM) were added to a colorless solution of RBTP (20 μM), as
shown in Fig. 3, only Pd2+ could induce a distinct fluorescence enhancement at 584
nm and color change from colorless to pink, whereas other metal ions were not
observed. All this results demonstrated that sensor RBTP has high selectivity to Pd2+.
Fig. 3. Fluorescence spectral changes of sensor RBTP (20 μM) upon addition of Pd2+ (100 μM)
and various other metal ions (100 μM, respectively) in the EtOH/H2O solution (3/2, v/v, pH 7.4,
HEPES buffer, 0.5 mM). λex = 562 nm, λem = 584 nm
3.4. Sensitive response of sensor RBTP to Pd2+
To further demonstrate the sensitivity of sensor RBTP to palladium, fluorescence
titration experiments of RBTP with Pd2+ were carried out in EtOH/H2O solution (3/2,
v/v, pH 7.4, HEPES buffer, 0.5 mM). As shown in Fig. 4, upon the addition of Pd2+
(0-10 equiv.) to RBTP (20 μM), it can be obviously observed that the fluorescence
intensity of RBTP enhance gradually. However, the fluorescence intensity of RBTP
almost did not change after addition of Pd2+ is 8 equiv. A great linear relationship was
found between the concentration of Pd2+ from 0 to 40 μM and the fluorescence
intensity of RBTP at 584 nm: y = 9320.05644 x+ 5207.2038 (R2=0.98952, Fig. S2),
where y was the fluorescence intensity of RBTP at 584 nm and x was the concen-
tration of Pd2+. The detection limit was calculated to be 49.5 nM according to the
equation: detection limit = 3σ/κ. The fluorescence spectrum of RBTP was measured
10 times, then the standard deviation (σ) was calculated (table 1 in supporting
information) , and κ is the slope of the intensity ratio versus sample concentration plot,
which indicated that sensor RBTP has significant sensitivity to detect Pd2+
quantitatively.
Based on fluorescence titration, the association constant value (Ka) of sensor
RBTP for Pd2+ was calculated as 1.15 × 104 M-1 (Fig. S3), and according to the

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Benesi-Hildebrand equation: F – F0 = ΔF = [Pd2+] (Fmax – F0)/(1/Ka + [Pd2+]), where F
is the emission intensity at 584 nm, F0 is the emission intensity of sensor RBTP at 584
nm, Fmax is the emission intensity of sensor RBTP when fully integrated with Pd2+ at
584 nm. The Job’s plot revealed 1:1 complexation stoichiometry between sensor
RBTP and Pd2+ (Fig. S4), which indicated the binding mode of sensor RBTP and
Pd2+.
Fig. 4. Fluorescence spectral changes of sensor RBTP (20 μM) upon addition of different
concentrations of Pd2+ (0-10 equiv.) in the EtOH/H2O solution (3/2, v/v, pH 7.4, HEPES buffer,
0.5 mM). Inset: the saturation curve of fluorescence intensity changes. λex = 562 nm, λem = 584 nm
3.5. Competition experiments
To further investigated the selectivity of sensor RBTP to Pd2+, competition experi-
ments were performed in EtOH/H2O solution (3/2, v/v, pH 7.4, HEPES buffer, 0.5
mM) by adding different metal ions (5 equiv., 100 μM) to the solution of sensor RBTP
(20 μM) in the presence of Pd2+ (5 equiv., 100 μM) as shown in Fig. 5. All results
indicate that the fluorescence intensity of sensor RBTP to Pd2+ at 584 nm have not
generated obviously quenching in the presence of other competitive metal ions. Hence,
sensor RBTP has a high selectivity in the recognition Pd2+ even if in the presence of
other competitive metal ions.
Fig. 5. Competition experiments of sensor RBTP (20 μM) to Pd2+ (100 μM) in EtOH/H2O

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solution (3/2, v/v, pH 7.4, HEPES buffer, 0.5 mM) in the presence of 5 equiv. of other
metal ions, respectively. λex = 562 nm, λem = 584 nm
3.6. pH response of sensor RBTP
The pH response of sensor RBTP was measured based on acid base titration exper-
iments in EtOH/H2O solution (3/2, v/v, pH 7.4, HEPES buffer, 0.5 mM). As shown in
Fig. S5, the sensor RBTP did not emit fluorescence at 584 nm in the wide pH range
6-12 and the fluorescence intensity of sensor RBTP at 584 nm became gradually
steady at pH<3. All results indicated that sensor RBTP should detect Pd2+ in the range
of pH 6-12.
3.7. Response time of sensor RBTP to Pd2+
Response time of sensor RBTP to Pd2+ was conducted in the wide time range 0-50
min. The results were shown in Fig. S6, within 40 min when Pd2+ was added, the
fluorescence intensity of sensor RBTP at 584 nm increased slowly and reached the
maximum value.
3.8. MS spectra study
In order to further confirm the binding mechanism of sensor RBTP to Pd2+, the
mass spectrum of sensor RBTP was measured in the absence and presence of Pd2+.
The peaks at m/z 743.3 and m/z 847.3 were attributed to [RBTP+H]+ and [RBTP2-+
Pd2++H+]+, respectively(Fig. S7 and Fig. S17). It suggested 1:1 complexation stoich-
io metry between sensor RBTP and Pd2+, which is consistent with the Job's plot
analysis.
3.9. Test papers
To evaluate the practical application of sensor RBTP for detection of Pd2+, test
papers were made. Filter papers were dipped in stock solution with RBTP (1 mM),
and dried in air. Then the filter papers with RBTP were exposed to different
concentrations of Pd2+ for several minutes and dried in the air. Last test papers were
observed with a rapid color change from colorless to pink under 365 nm UV light. As
shown in Fig. 6, it was indicated that sensor RBTP could be made as test paper to
ration detect for Pd2+.

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Fig. 6. Photographs of test papers treated with various concentrations of Pd2+
3.10. The proposed sensing mechanism
To further research the possible binding mechanism of sensor RBTP with Pd2+, we
conducted density functional theory (DFT) study with the B3LTP/6-31G(d, p) method.
The spatial distributions and orbital energies of the HOMO and LUMO of RBTP and
RBTP-Pd2+ complex were investigated and shown in fig. 7. The HOMO-LUMO
energy gaps of RBTP and RBTP-Pd2+ were respectively calculated to be 393.6
KJ/mol and 214.5 KJ/mol, which indicate that the interaction of sensor RBTP and
Pd2+ resulted in the disruption of the photoinduced electron transfer (PET). The DFT
calculations have further confirmed that the process of RBTP-Pd2+ complex formation
involves the corresponding oxygen and nitrogen atoms of sensor RBTP in the coordi-
nation of Pd2+, as shown in scheme 2.
Fig. 7. HOMO and LUMO orbitals of RBTP and RBTP-Pd complex

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Scheme 2. The possible binding mode of sensor RBTP with Pd2+
4. Conclusions
In summary, we have designed and synthesized a new colorimetric and fluorescent
sensor RBTP to sequentially recognize palladium (II) in aqueous solution. Sensor
RBTP shows high sensitivity and selectivity, quick response, color change and
significant fluorescence turn-on response. In addition, the crystal structure of RBTP
was supported by X-ray diffraction. Furthermore, sensor RBTP could be made as test
paper for quantitative detection of Pd2+.
Acknowledgements
This work was supported by Qing Lan Project of Jiangsu Province.
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Graphical abstract
A new rhodamine B and purine-based colorimetric and fluorescent sensor RBTP
was prepared and structurally characterized to sequentially recognize palladium (II).
Sensor RBTP shows high sensitivity and selectivity, quick response, colour change
and significant fluorescence turn-on response for recognition and detection of Pd2+.

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Highlight
Some of the important highlights of this work are following:
1. RBTP is used as a fluorescent sensor for selective and quantitative detection of palladium with
a quite low the limit of detection as 49.5 nM.
2. RBTP is highly selective to palladium without interference from other cations.
3. RBTP detects palladium under mild condition (pH>6) in aquenous solution.
4. The crystal structure of RBTP was supported by X-ray diffraction.
5. RBTP can be made as a test paper to ration detect for palladium.