A reversible fluorescent chemosensor for mercury ions based on 1H-imidazo[4,5-b]phenazine derivatives

DOI: 10.1016/j.tet.2013.07.007

Source and publish data:

Tetrahedron p. 7981 - 7987 (2013)

Update date:2022-07-30

Topics:

Authors:

Shi, Bingbing

Zhang, Peng

Wei, Taibao

Yao, Hong

Lin, Qi Lin, Qi

Liu, Jun

Zhang, Youming

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Article abstract of DOI:10.1016/j.tet.2013.07.007

A series of non-sulfur, fluorescent sensors (S₆, S_6-1 or S_6-2) for mercury ions bearing 1H-imidazo[4,5-b]phenazine derivatives have been designed and synthesized. Among these sensors, a furan group into the sensor S₆ molecule was as the functional group, compound S_6-1 containing the 5-(4-Nitrophenyl)-2-furan group was synthesized, and in order to establish the furan group's contribution to the sensor's fluorescent sensing abilities, compound S_6-2, which without containing the furan group was also synthesized. S₆ showed excellent fluorescent specific selectivity and high sensitivity for Hg²⁺ in aqueous solution. The detection limit of the sensor towards Hg²⁺ is 1.6×10^-7 M, and other ions, including Fe³⁺, Ca ²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd ²⁺, Pb²⁺, Zn²⁺, Cr³⁺, and Mg ²⁺ had nearly no influence on the probing behavior. Notably, this sensor serves as a recyclable component in sensing materials. The test strips based on S₆ were fabricated, which could act as a convenient and efficient Hg²⁺ test kits.

Full text of DOI:10.1016/j.tet.2013.07.007

Accepted Manuscript

A reversible fluorescent chemosensor for Mercury ions based on 1H-Imidazo[4,5-

b]Phenazine derivatives

BingBing Shi, Peng Zhang, TaiBao Wei, Hong Yao, Qi Lin, Jun Liu, YouMing Zhang

PII:

S0040-4020(13)01088-0

10.1016/j.tet.2013.07.007

TET 24588

DOI:

Reference:

To appear in: Tetrahedron

Received Date: 15 April 2013

Revised Date: 19 June 2013

Accepted Date: 3 July 2013

Please cite this article as: Shi B, Zhang P, Wei T, Yao H, Lin Q, Liu J, Zhang Y, A reversible fluorescent

chemosensor for Mercury ions based on 1H-Imidazo[4,5-b]Phenazine derivatives, Tetrahedron (2013),

doi: 10.1016/j.tet.2013.07.007.

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Graphical abstract

reversible fluorescent

1H-Imidazo[4,5-b]Phenazine derivatives

chemosensor

for

Mercury

ions

based

BingBing Shi, Peng Zhang, TaiBao Wei, Hong Yao, Qi Lin, Jun Liu, YouMing Zhang*

Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Educati on of China; Key

Laboratory of Polymer Materials of Gansu Province; College of Chemistry and Chemical Engineering,

Northwest Normal University, Lanzhou, Gansu, 730070，P. R. China

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A reversible fluorescent chemosensor for Mercury ions based on

1H-Imidazo[4,5-b]Phenazine derivatives

BingBing Shi, Peng Zhang, TaiBao Wei, Hong Yao, Qi Lin, Jun Liu, YouMing Zhang*

-------------------------------------------

E-mail: zhangnwnu@126.com¹

-------------------------------------------

Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Educati on of

China; Key Laboratory of Polymer Materials of Gansu Province; College of Chemistry and

Chemical Engineering, Northwest Normal University, Lanzhou, Gansu, 730070

，P. R. China

Abstract:

A series of non-sulfur, fluorescent sensors (S₆, S_6-1or S_6-2) for mercury ions bearing

1H-Imidazo[4,5-b]Phenazine derivatives have been designed and synthesized. Among

there sensors, a furan group into the sensor S₆molecule was as the functional group,

compound S_6-1containing the 5-(4-Nitrophenyl)-2-furan group was synthesized, and in

order to establish the furan group’s contribution to the sensor’s fluorescent sensing

abilities, compound S_6-2which without containing the furan group was also synthesized.

S₆showed excellent fluorescent specific selectivity and high sensitivity for Hg²⁺in

aqueous solution. The detection limit of the sensor towards Hg²⁺is 1.6×10^-7M, and

other ions, including Fe³⁺, Ca²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺, and Mg²⁺

had nearly no influence on the probing behavior. Notably, this sensor serves as a

recyclable component in sensing materials. The test strips based on S₆were fabricated,

which could act as a convenient and efficient Hg²⁺test kits.

*Corresponding author

Tel: +086 9317973191; E-mail address: zhangnwnu@126.com (Y-M Zhang)

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Keywords: non-sulfur, fluorescent, phenazine, mercury ions, recyclable, test kits

1. Introduction

Mercury is one of the most hazardous species in nature, which may cause prenatal

brain damage, cognitive and motion disorders, vision and hearing loss, and even

death.¹Development of a facile and selective method for Hg²⁺detection has long been

demanded in the area of food safety and environmental protection. Numerous

chemosensors for Hg²⁺with good properties have been reported.²Most of these

traditional chemosensors contain a sulfur moiety and the sensing process involves an

irreversible coordination of Hg²⁺to the S atom.³The mechanism for traditional

sensors includes an affinity irreversible organic reaction driven by the extremely

strong Hg–S affinity. (1) ring opening of spirocyclic systems (rhodamine and

fluorescein, etc.),⁴(2) intramolecular cyclic guanylation of thiourea derivatives,⁵(3)

conversion of thiocarbonyl compounds into their carbonyl analogues or a sequential

desulfurization-lactonization reaction⁶(Scheme 1). This thiophilic approach will suffer

from potential interference in sulfur-rich environments where mercury is abundant,⁷

Scheme 1 Tactics for the sensing of Hg²⁺.

and undesired oxidation of the probes containing a sulfur atom by air or oxidizing

reagents also inevitably occurs. Other drawbacks may be the requirement for elevated

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temperature or excess quantities of Hg²⁺to drive these desulfurization reactions to

completion. Correspondingly, most of the traditional chemosensors which contain a

sulfur moiety and the sensing process involves an irreversible coordination of Hg²⁺to

the S atom were unrecyclable. So the recyclable sensors for Hg²⁺are badly needed.

Furthermore, phenazine derivatives have been synthesized and been used for

organic electronics for a long time,⁸but they have seldom been used in host-guest

chemistry. Phenazines are ideal platforms for the development of cation, anion, and

neutral molecule recognition. Moreover, among the different fluorogenic units,

phenazine is very sensitive to conformational change. Phenazine-based fluorescent

chemosensors are still very scarce, although in principle, well-designed ones should

show very good performance.

In view of this requirement and as part of our research effort devoted into ion

recognition,⁹an attempt was made to obtain a non-sulfur, recyclable and efficient

fluorescent sensor which could sense Hg²⁺with specific selectivity and high

sensitivity in aqueous solution. This paper details the design and synthesis of a series

of Hg²⁺fluorescent sensors S₆, S_6-1or S_6-2bearing 1H-Imidazo[4,5-b]Phenazine

derivatives (Scheme 2). The strategies for the design of these sensors were as follows.

The phenazine group acts as fluorophore, imidazole and furan groups into the same

sensor molecule as the functional groups, to allow the coordination capacity required

to coordinate a mercury ion. The sensors were designed to be easy to synthesize. In

order to establish the substituent group’s influence to the sensor’s fluorescent sensing

abilities for Hg²⁺, compound S_6-1which containing the 5-(4-Nitrophenyl)-2-furan

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group was synthesized, and in order to establish the furan group’s contribution to the

sensor’s fluorescent sensing abilities for Hg²⁺, compound S_6-2which without

containing the furan group was also synthesized. Sensor S₆showed fluorescent

selectivity for mercury ions in DMSO/H₂O (6:4, v/v) HEPES buffer solutions

(pH=7.2) over other common physiologically important metal ions. To the best of our

knowledge, this is the first time that the Phenazine derivatives were used to the

recognition of Hg²⁺ions with high selectivity.

Scheme 2 Synthesis of compounds S₆, S_6-1and S_6-2

2. Experimental

2.1. Materials and physical methods

Fresh double distilled water was used throughout the experiment. All other reagents

and solvents were commercially available at analytical grade and were used without

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further purification. ¹H NMR spectra were recorded on a Mercury-400BB

spectrometer at 400 MHz and C NMR spectra were recorded on a Mercury-600BB

spectrometer at 150 MHz. Chemical shifts are reported in ppm downfield from

tetramethylsilane (TMS, δ scale with solvent resonances as internal standards)

Melting points were measured on an X-4 digital melting-point apparatus (uncorrected).

Infrared spectra were performed on a Digilab FTS-3000 FT-IR spectrophotometer.

2.2. Synthesis of sensors S₆, S_6-1and S_6-2.

2,3-diamino-phenazine was prepared following the reported procedure.⁸

5-(4-Nitrophenyl)-2-furaldehyde was prepared following the reported procedure.¹⁰

Synthesis of Compounds S₆, S_6-1and S_6-2:

2,3-diamino-phenazine (0.42g, 2mmol), 2-furaldehyde (0.24g, 2.5mmol) and

catalytic amount of acetic acid (AcOH) were combined in hot absolute DMF (20 mL).

The solution was stirred under reflux conditions for 8 hours, after cooling to room

temperature, the brown precipitate was filtrated, washed with hot absolute ethanol

three times, then recrystallized with DMF-H₂O to get brown powdery product S₆. The

other compounds S_6-1and S_6-2was prepared by similar procedures.

S₆: Yield: 72%; m.p.>300℃; H NMR (DMSO-d₆, 400 MHz) δ 13.43 (s 1H), δ 8.45

(s 1H), 8.23~8.21 (m 3H), 8.17~8.16 (d J=4 1H), 7.90~7.87 (m 2H), 7.59~7.58 (d J=4

1H), 6.89~6.88 (m 1H); ¹³C-NMR (DMSO-d₆, 150 MHz) δ 156.16, 154.46, 151.15,

147.08, 144.39, 141.77, 141.03, 140.13, 136.99, 129.76, 129.09, 128.58, 123.20,

115.04, 113.15, 102.37, 99.07; IR (KBr, cm^-1) v: 3101 (NH), 1653 (C=N), 1620

(C=C); ESI-MS m/z: (M+H)⁺Calcd for C₁₇H₁₀N₅O 287.2; Found 287.2; Anal. Calcd.

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For C₁₇H₁₀N₅O: C, 71.32; H, 3.52; N, 19.57; O, 5.59; Found C, 71.26; H, 3.55; N,

19.56; O, 5.63.

S_6-1: Yield: 75%; m.p.>300℃; H NMR (DMSO-d₆, 400 MHz) δ 13.56 (s 1H), δ

8.34~8.32 (m 3H), 8.18~8.15 (m 5H), 7.84~7.81 (m 2H), 7.67~7.66 (d J=4 1H),

7.61~7.60 (d J=4 1H); IR (KBr, cm^-1) v: 3106 (NH), 1643 (C=N); ESI-MS m/z:

(M+H)⁺Calcd for C₂₃H₁₃N₅O₃408.3; Found 408.4; Anal. Calcd. For C₂₃H₁₃N₅O₃: C,

67.81; H, 3.22; N, 17.19; O, 11.78; Found C, 67.78; H, 3.24; N, 17.16; O, 11.82.

S_6-2: Yield: 80%; m.p.>300℃; ¹H NMR (DMSO-d₆, 400 MHz) δ 13.44 (s 1H), δ 8.51

(s 1H), 8.38~8.37 (d J= 4 2H), 8.26~8.23 (d 3H), 7.89~7.88 (d J=4 2H), 7.67~7.66 (d

3H); ¹³C-NMR (DMSO-d₆, 150 MHz) δ 159.55, 148.88, 141.87, 141.68, 140.51,

140.23, 139.84, 131.87, 131.88, 129.85, 129.55, 129.23, 129.22, 129.02, 128.80,

127.76, 127.75, 114.84, 105.91; IR (KBr, cm^-1) v: 3168 (NH), 1693 (C=N); ESI-MS

m/z: (M+H)⁺Calcd for C₂₃H₁₃N₅O₃297.1; Found 297.2; Anal. Calcd. For C₂₃H₁₃N₅

O₃: C, 77.01; H, 4.08; N, 18.91; Found C, 77.08; H, 4.04; N, 18.88.

2.3. General procedure for Fluorescence spectra experiments

All fluorescence spectra were recorded on a Shimadzu RF–5301 fluorescence

spectrometer after the addition of perchlorate metal salts in DMSO, while keeping the

ligand concentration constant (2.5 × 10^-5M). The excitation wavelength was 416 nm.

Solutions of metal ions were prepared from the perchlorate salts of Fe³⁺, Hg²⁺,

Ca²⁺,Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺, and Mg²⁺.

2.4. General procedure for ¹H NMR experiments

For H NMR titrations, two stock solutions were prepared in DMSO-d₆, one

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containing the sensor only and the second containing an appropriate concentration of

the metal. Aliquots of the two solutions were mixed directly in NMR tubes.

3. Results and discussion

In order to investigate the Hg²⁺recognition abilities of the sensors S₆, S_6-1and S_6-2in

aqueous solution, we carried out a series of Host-Guest recognition experiments in

DMSO/H₂O (6:4/v:v) HEPES buffered solution at pH 7.2. The fluorescent

measurements for S₆, S_6-1and S_6-2were first performed in DMSO/H₂O (6:4/v:v)

HEPES buffered solution (pH=7.2). As shown in Figure (1), sensors S₆and S_6-2had

strong emission maximum wavelength at 546 nm and 544 nm, but S_6-1emitted very

weakly, indicating that the 5-aryl-furan unit directly bound to the phenazine group

quenched the emission for the formation of the twisted intramolecular charge transfer

state.¹¹The recognition

Figure 1 Fluorescence spectra of S₆(25ꢀΜ), S_6-1(25ꢀΜ) or S_6-2(25ꢀΜ).

profiles of the chemosensor S₆toward various metal cations, Fe³⁺, Hg²⁺, Ca²⁺, Cu²⁺,

Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺, and Mg²⁺, were investigated by fluorescence

spectroscopy in DMSO/H₂O (6:4/v:v) HEPES buffered solution at pH 7.2. As shown

in Figure (2), in the fluorescence spectrum, the emission of S₆appeared at the

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maximum emission wavelength was 546 nm in DMSO/H₂O (6:4, v/v) HEPES buffer

(pH 7.2) solution when excited at λ_ex=416 nm. When 15 equivalents of Hg²⁺was

Figure 2 Fluorescence spectra of S₆upon an excitation at 416 nm in DMSO/H₂O (PH=7.2,

v/v=6:4) in the presence of Hg²⁺(15 equiv.). Inset: photograph from left to right shows the change

in the fluorescence of S₆, S₆-Hg²⁺(15 equiv.) in DMSO/H₂O (PH=7.2, v/v=6:4).

Figure 3 (a) Fluorescence emission data for a 1:15 mixture of S₆(25ꢀM) and different metal ions:

1)only S₆, 2) Fe³⁺, 3) Hg²⁺, 4) Ca²⁺, 5) Cu²⁺, 6) Co²⁺, 7) Ni²⁺, 8) Cd²⁺, 9) Pb²⁺, 10) Zn²⁺, 11) Cr³⁺

and 12) Mg²⁺; as their perchlorate salts, in DMSO/H₂O (PH=7.2, v/v=6:4) solution. (excitation

wavelength = 416 nm). (b) Visual fluorescence emissions of sensor S₆after the addition of Fe³⁺,

Hg²⁺, Ca²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺and Mg²⁺(15 equiv.) in DMSO/H₂O (PH=7.2,

v/v=6:4) on excitation at 365 nm using UV lamp at room temperature.

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added to the DMSO/H₂O (6:4, v/v) HEPES buffer (pH 7.2) solutions of sensor S₆, the

fluorescence emission band at 546 nm is red-shifted to 562 nm. The apparent

fluorescence emission color change from yellow to jacinth could be distinguished by

the naked eye. To validate the selectivity of sensor S₆, the same tests were also

applied using Fe³⁺, Ca²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺, and Mg²⁺ions, and

none of these anions induced any significant changes in the fluorescent spectrum of

the sensor (Figure 3). Therefore, in DMSO/H₂O solution, S₆showed specific

Figure 4 Fluorescence emission data for a 1:15 mixture of S_6-1(25ꢀM) and different metal ions:

1)only S₆, 2) Fe³⁺, 3) Hg²⁺, 4) Ca²⁺, 5) Cu²⁺, 6) Co²⁺, 7) Ni²⁺, 8) Cd²⁺, 9) Pb²⁺, 10) Zn²⁺, 11) Cr³⁺

and 12) Mg²⁺; as their perchlorate salts, in DMSO/H₂O (PH=7.2, v/v=6:4) solution. (excitation

wavelength = 436 nm).

fluorescent selectivity to Hg²⁺. The same tests were applied to S_6-1(Figure 4) and S_6-2

(Figure 5). In this case, when various cations were added to the DMSO/H₂O (6:4/v:v,

pH=7.2) solutions of S_6-1or S_6-2, no obvious changes were observed. In corresponding

fluorescent spectrum of S_6-1or S_6-2, there is no selectivity for the recognition of Hg²⁺,

which indicated that S_6-1or S_6-2couldn’t fluorescent and selectively sense Hg²⁺under

these conditions.

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Figure 5 Fluorescence emission data for a 1:15 mixture of S_6-2(25ꢀM) and different metal ions:

1)only S₆, 2) Fe³⁺, 3) Hg²⁺, 4) Ca²⁺, 5) Cu²⁺, 6) Co²⁺, 7) Ni²⁺, 8) Cd²⁺, 9) Pb²⁺, 10) Zn²⁺, 11) Cr³⁺

and 12) Mg²⁺; as their perchlorate salts, in DMSO/H₂O (PH=7.2, v/v=6:4) solution. (excitation

wavelength = 403 nm).

Therefore, according to these results we can find that the furan moiety acted as a

functional group and played a crucial role in the process of colorimetric recognition.

The sensor S₆employ furan moiety as functional group, which possess fluorescent

response abilities for Hg²⁺cations. Because the S_6-1employ the

5-(4-Nitrophenyl)-2-furan group as functional group, and the nitrophenyl group in the

molecule can enhance the the twisted intramolecular charge transfer ability, the

fluorescent capability of S_6-1is too weak to fluorescent recognize any cations.¹²At the

same time, because the S_6-2has no furan unit as functional group, S_6-2has no

fluorescent capability to fluorescent recognize any cations.

As S₆showed specific selectivity for Hg²⁺, a series of experiments was carried out to

investigate the Hg²⁺recognition capability and mechanism of S₆. To gain an insight

into the stoichiometry of the S₆-Hg²⁺complex, the method of continuous variations

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Figure 6 The Job’s plot examined between Hg²⁺and S₆, indicating the 1 : 1 stoichiometry for

S₆-Hg²⁺clearly.

(Job’s method)¹³was used. When the molar fraction of sensor S₆was 0.5, the

fluorescence intensity value approached a maximum, which demonstrated the

formation of a 1:1 complex between the sensor S₆and Hg²⁺(Figure 6).

Figure 7 (a) Fluorescence spectra of S₆(25ꢀM) in the presence of different concentration of Hg²⁺

(0-5.58 equiv.) in DMSO/H₂O (PH=7.2, v/v=6:4). (b) A plot of fluorescence intensity depending

on the concentration of Hg²⁺in the range from 0 to 5.58 equivalents.

The binding properties of sensor S₆with Hg²⁺were further studied by fluorescence

emission spectral variation experiments (Figure 7). It turned out that DMSO/H₂O

(6:4/v:v, pH=7.2) solutions of S₆, with an increasing amount of Hg²⁺, the emission peak

at 546 nm gradually shifted to 562 nm. The binding constant Ks of the metal complex

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was determined as 1.8×10⁴M^-1. And the detection limit of the fluorescent spectrum

changes calculated as 1.6×10^-7M for Hg²⁺cation, which pointing to the high detection

sensitivity.

Figure 8 IR spectra of compound S₆and S₆-Hg²⁺complex in KBr disks.

The recognition mechanism of the sensor S₆with Hg²⁺were investigated by IR

spectra and ¹H NMR titration methods. In the IR spectra of S₆, the stretching vibration

absorption peaks of imidazole N-H, imidazole C=N and furan C=C appeared at 3100,

1651 and 1625 cm^-1respectively. However, when S₆coordinated with Hg²⁺, the

stretching vibration absorption peaks of imidazole N-H shifted to 3124 cm^-1, while, the

stretching vibration absorption peaks of imidazole C=N and furan C=C shifted to 1618

cm^-1, which indicated that S₆complexed with Hg²⁺via O-Hg²⁺-N coordination bond as

shown in Figure (8).

The results of H NMR titration experiments also support this presumption. As

shown in Figure (9), after adding 1.0 equivalents of Hg²⁺, the NH peak at 13.4 ppm

disappeared. At the same time, the signal of the hydrogen atoms in the benzene and

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S₆+2equiv. Hg²⁺+4equiv. I^-

Up field shift

S₆+2equiv. Hg²⁺

Down field shift

Only S₆

Figure 9 H NMR spectra (400 MHz, DMSO-d₆) of free S₆and in the presence of Hg²⁺, I^-,

respectively.

furan rings showed a significant downfield shift, indicating a charge transfer from the

benzene and furan groups to the Hg²⁺ions. After adding 2.0 equivalents of I^-to the

above system, one new peak appeared at 8.8 ppm, which can be attributed to the NH

protons. Because of the negative electron character of I^-, the N-H signal in the top line

and bottom line is different.¹⁴And, the signal of the hydrogen atoms in the benzene

and furan rings showed a significant upfield shift. Based on the above findings, we

propose that the reaction mechanism in this system may proceed through the route

depicted in Figure (10).

Figure 10 The proposed structures of S₆for Hg²⁺and I^-ions.

An important feature of the sensor is its high selectivity toward the analyte over other

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competitive species. The variations of fluorescent spectrum of sensor S₆in DMSO/H₂O

binary solutions caused by the metal ions Fe³⁺, Ca²⁺, Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺,

Cr³⁺, and Mg²⁺were recorded in Figure (3). It is noticeable that the miscellaneous

competitive metal ions did not lead to any significant interference. In the presence of

these ions, the Hg²⁺still produced similar emission changes (Figure 11). These results

shown that the selectivity of sensor S₆toward Hg²⁺was not affected by the presence of

other cations and suggested that it could be used as a fluorescent chemosensor for Hg²⁺.

Figure 11 Fluorescence spectra of S₆and S₆-Hg²⁺in the presence of 15 equivalents of various

metal ions in DMSO/H₂O (PH=7.2, v/v=6:4) HEPES buffered solution at pH 7.2, room

temperature.

The selectivity of S₆to Hg²⁺was also examined over a wide range of pH values.

No apparent changes of the fluorescence spectra were observed, and the detection of

Hg²⁺can work well in the range of pH 2.0-10.0 (Figure 12).

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Figure 12 Influence of pH on the fluorescence of S₆-Hg²⁺in DMSO/H₂O (PH=7.2, v/v=6:4).

Excitation wavelength is 416 nm.

Figure 13 Emission spectra showing the reversible complexation between S₆and Hg²⁺(5.0 equiv.)

by introduction of I^-(10.0 equiv.).

The reversibility of the chemosensor function was tested by addition of I^-to the

mercury-sensor complex. The I^-ion is well-known to bind strongly to Hg²⁺ions.¹⁵

Addition of I^-to a solution of the S₆–Hg²⁺complex induced the opposite trend in the

fluorescent spectra to that observed on titration with Hg²⁺. Upon addition of 40

equivalents of I^-, the optical fluorescence intensity returned to the levels observed for

the free compound S₆. The addition of I^-to the S₆–Hg²⁺complex shows that the

process of titrating sensor S₆with Hg²⁺is reversible, and the reversible process could

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be repeated at several times with little fluorescent efficiency loss (Figure 13, 14).

Figure 14 Fluorescence emission spectra of S₆(25ꢀM) in the presence of Hg²⁺(15 equiv.) or I^-

(40 equiv.) in DMSO/H₂O (PH=7.2, v/v=6:4) solution. The excitation wavelength was 416 nm.

Inset: photograph from left to right shows the change in the fluorescence of only S₆, S₆-Hg²⁺(15

equiv.) and S₆-Hg²⁺(15 equiv.) plus I^-(40 equiv.) in DMSO/H₂O (PH=7.2, v/v=6:4) solution on

excitation at 365 nm.

To investigate the practical application of chemosensor S₆, test strips were prepared

by immersing filter papers into a DMSO solution of S₆(0.1 M) and then drying in air.

The test strips containing S₆was utilized to sense Hg²⁺and other metal ions. As

shown in Figure (15), when Hg²⁺and the other ions were added on the test kits

respectively, the obvious color change was observed only with Hg²⁺solution under

the 365nm UV lamp. And potentially competitive ions exerted no influence on the

detection of Hg²⁺by the test strips. Therefore, the test strips could conveniently detect

Hg²⁺in solutions.

Figure 15 Photographs of S₆on test papers (A) only S₆, (B) after immersion into DMSO/H₂O

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(PH=7.2, v/v=6:4) solutions with Hg²⁺, C) after immersion into DMSO/H₂O (PH=7.2, v/v=6:4)

solutions with others ions, (D) after immersion into DMSO/H₂O (PH=7.2, v/v=6:4) solutions with

Hg²⁺and other ions under irradiation at 365 nm.

4. Conclusion

A non-sulfur, recyclable sensor S₆of mercury ions has been designed and

synthesized. The sensor was bearing 1H-Imidazo[4,5-b]Phenazine derivatives, which

shown brilliant fluorescent response for Hg²⁺ions in aqueous solution. The detection

limit of the sensor towards Hg²⁺is 1.6×10^-7M, and other ions, including Fe³⁺, Ca²⁺,

Cu²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺, and Mg²⁺had nearly no influence on the

probing behavior. Notably, this sensor serves as a recyclable component in sensing

materials. In addition, test strips based on S₆were fabricated, which also exhibits a

good selectivity to Hg²⁺as in solution. We believe the test strips could act as a

convenient and efficient Hg²⁺test kit.

Acknowledgment

This work was supported by the National Natural Science Foundation of China (No.

21064006, 21262032 and 21161018), the Program for Changjiang Scholars and

Innovative Research Team in University of Ministry of Education of China (No.

IRT1177), the Natural Science Foundation of Gansu Province (No. 1010RJZA018),

the Youth Foundation of Gansu Prov-ince (No. 2011GS04735) and

NWNU-LKQN-11-32.

Supplementary data

These data include the Spectral data, MS data and copies of H/¹³C NMR of the

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compounds described in this article. Supplementary data associated with this article

can be found in the online version.

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List of Figures and schemes: