English

• 1.   Introduction

  The sensing and detection of hazardous substances plays an important role in life and environmental sciences. The past decade has witnessed a fast growth for detection of Fe³⁺ ion because massive utilization of Fe³⁺ ion causes environmental pollution and health problems.^[1~7] It is well known that the Fe³⁺ ion plays an important role in biological metabolism and are recognized as an industrial pollutant. However, these widely used instrumental analytical techniques have some limitations, including expensive equipment, complication in sample preparation and well-trained person. To defeat this problem, the large number of well-designed sensors based on this Fe³⁺ ion have been developed by fluorescent^[8~18] and colorimetric^[19] sensing methods, of which sensitive and selective detections of Fe³⁺ ion by fluorescent methods are most competitive and have attracted great attention in recent years. Although metal-organic frameworks (MOFs) as fluorescent probe have been widely investigated for their potential application in the sensitive and selective detection of Fe³⁺ ion, many MOFs are limited in wide application due to complicate operations, slow signal response, poor stability, ^[20] expensive raw materials, ^[21~24] toxic (including heavy metal)^{[25, 26]} and not suitable for aqueous and biological environment. In addition, though Zr⁴⁺ is not classified as one of the essential elements for human and cannot also produce toxic effects for environment, it is a rare metal and very important atomic energy elements which is widely used in military industry, smelting, atomic energy industry and battery.^{[27, 28]} However, up to now, there is only a small amount of detection of Zr⁴⁺ ion, ^[29] mostly the recognition of Fe³⁺ ion by Zr(Ⅳ)-MOFs.^{[30, 31]} Besides, MOFs are also used as fluorescent probes to detect small molecular compounds, such as H₂S, ^[32] biomolecules, ^[33] acetone^{[34, 35]} and nitroaromatic compounds.^[36~38] Therefore, there is an urgent need to develop a new chemosensor for the rapid selective and sensitive detection of Zr⁴⁺, Fe³⁺ ion and acetone as the replacement.

  In this work, it reports an organic fluorescent probe L (no heavy metal ions and low toxicity) which is rationally designed on the basis of 2, 4, 6-trichloro-1, 3, 5-triazine and contains nine coordination centers (Figure 1). It exhibits strong fluorescence and highly sensitive and selective toward Zr⁴⁺, Fe³⁺ ions and acetone in room temperature. With the addition of Fe³⁺ ion, compound L could give rise to a visible colorless-to-yellow change and clear fluorescence quenching. In contrast to this, with the addition of Zr⁴⁺ ion, the compound shows fluorescence enhancement. This is the first example of fluorescent organic compound chemosensor for the highly selective detection of Zr⁴⁺, Fe³⁺ ions and acetone simultaneously based on 1, 3, 5-triazine derivatives with the highest density of uncoordinated N and carboxylate O atoms. This study might provide a new method for the rapid detection of Zr⁴⁺, Fe³⁺ ions and acetone with the advantages of simple sample pretreatment processes, highly sensitive and selective sensing.

  Figure 1

  

  Figure 1.  Structure and fluorescent of L

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  2.   Results and discussion

  2.1   Metal ions detection

  The fluorescent properties of the sensor L in N, N-di- methylformamide (DMF) are measured at room temperature. L exhibits strong fluorescent emission at 415 nm. Furthermore, L is explored for the application in the detection of metal ions in DMF and water system based on fluorescent sensing. In the measurement, 1.2161 mg of freshly prepared samples of L are dissolved in 250 mL DMF solution (1×10^-5 mol•L^-1), to which is dropwise added different metal ions of aqueous solution. In this regard, the responses of the fluorescence of L/DMF solution toward 15 different metal cations (Zr⁴⁺, Fe³⁺, Co²⁺, Cr³⁺, Ni²⁺, Cu²⁺, Cd²⁺, Pb²⁺, Ag⁺, Sr²⁺, Ba²⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺) in aqueous solution were studied and obtained experimental data finally (Figure 2). Obviously, most cations display a negligible influence on fluorescence intensity of L. Specifically, the fluorescence intensity of L at 415 nm changes slightly while Co²⁺, Cr³⁺, Ni²⁺, Cu²⁺, Pb²⁺, Ag⁺, Sr²⁺, Ba²⁺, Ca²⁺, Na⁺ and K⁺ ions were added respectively. It can see clearly that is that the fluorescence intensity of L decreases significantly, to which is added Fe³⁺ ion. Conversely, the fluorescence intensity of L increases significantly while Zr⁴⁺ ion is added. In addition, the compound L could rapidly give rise to a visible colorless-to-yellow change after adding Fe³⁺ ion and the experiments show that yellow is not caused by the color of Fe³⁺ ion itself.

  Figure 2

  

  Figure 2.  Fluorescence spectra of L (2.9 mL, 1×10^-5 mol•L^-1) with different metal cations (0.1 mL, 10^-1 mol•L^-1) (λ_ex=365 nm)

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  2.1.1   Fe³⁺ ion detection

  To explore the complexation ratio of L (2.9 mL, 1× 10^-5 mol•L^-1) with Fe³⁺ ion in DMF solution, concentration-dependent experiments were further taken by UV method (Figure 3a). The absorption intensity of L gradually decreased with the increasing concentration of Fe³⁺ ion. The Job's curve was given according to the UV concentration curve of L and Fe³⁺ ions (Figure 3b). The results showed that the molar fraction of [Fe³⁺]/[L+Fe³⁺] was 0.4 when the curve had inflection point, demonstrating 2: 1 binding stoichiometry ration for L+Fe³⁺. Moreover, to evaluate the detection effects of L to Fe³⁺ ion, the fluorescence spectra of L in DMF (2.9 mL, 1×10^-5 mol•L^-1) with different concentrations of Fe³⁺ ion were carried out (Figure 4a). The experimental result showed that with the addition of different concentrations Fe³⁺ ion, the fluorescence intensity of L gradually decreases and shows a highly broad linear relationship with the concentration of Fe³⁺ ion from 1×10^-6 to 1×10^-5 mol•L^-1 expressed as an equation of y=41790.2576x+0.0406 and R=0.99905, where y is the ratio of (F₀-F)/F₀ and x is the concentration of Fe³⁺ ion. The other reported sensors for Fe³⁺ ion detection are generally within 1.25×10^-3 mol•L^-1 of Fe³⁺.^{[39, 40]} According to the fluorescence intensity of L, different concentration of Fe³⁺ and Benesi-Hildebrand equation, the detection limit of Fe³⁺ in L solution is calculated to be 1.33×10^-6 mol/L (Figure 4b).

  Figure 3

  

  Figure 3.  (a) UV-vis spectra of L with different concentration Fe³⁺ and (b) Job's plot of L with Fe³⁺

  (a) [L]=2.9 mL, 1×10^-5 mol•L^-1; [Fe³⁺]=0.1 mL, 1×10^-6~10×10^-5 mol•L^-1. (b) complexation ratio of L and Fe³⁺, [Fe³⁺]=0.1 mL, 1× 10^-6~10×10^-5 mol•L^-1

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  Figure 4

  

  Figure 4.  Fluorescence spectra (a) of L with different concentration Fe³⁺ and detection limit (b) of L with Fe³⁺ (λ_ex=324 nm)

  (a) [L]=2.9 mL, 1×10^-5 mol•L^-1; [Fe³⁺]=0.1 mL, 1×10^-6~10×10^-6 mol• L^-1; (b) Detection limit of Fe³⁺, [Fe³⁺]=0.1 mL, 1×10^-6~10× 10^-6 mol•L^-1

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  Obviously, the addition of different concentration Fe³⁺ ion to the DMF solution of L could give rise to a visible colorless-to-yellow change, and clear fluorescence quen- ching while the concentration of Fe³⁺ is up to 10×10^-3 mol•L^-1 (Figure 5). The initial fluorescence intensity of L (1×10^-5 mol•L^-1) was decreased by 99.9% when only 0.1 mL (1×10^-1 mol•L^-1) Fe³⁺ was added. Further, the quenching efficiency can be rationalized by the Stern- Volmer (SV) equation, F₀/F=1+K_SV[M], where F₀ and F are the relative fluorescence intensity before and after adding Fe³⁺, [M] is the molar concentration of the Fe³⁺ ion, and K_SV (L•mol^-1) is the Stern-Volmer quenching constant. The K_SV (Fe³⁺) value is calculated as 7.111×10⁴ L•mol^-1, suggesting a strong quenching effect on fluorescence. Under the same conditions, the quenching constants of other metals are shown in Table 1. The reason of fluo-rescence quenching may be that when Fe³⁺ and L form 2: 1 complex, the structure is isomerized, the imine (NH) bond is broken, and the bond length is shortened, which makes ligand L show color change when encountering Fe³⁺ ions. And there may be electron and energy transfer between the paramagnetism of Fe³⁺ and the unfilled d orbital in L, which makes the fluorescence quenching. Meanwhile, the antijamming experiments of Fe³⁺ ion specifically demonstrate that L can detect Fe³⁺ ion in the presence of other metal ions (Co²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Ag⁺, Sr²⁺, Ba²⁺, Ca²⁺, Na⁺, K⁺, Cd²⁺, Mg²⁺, Cr²⁺) (Figure 6).

  Figure 5

  

  Figure 5.  Photograph of L containing different concentrations of Fe³⁺ ion

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  Table 1

  

  Table 1.  Quenching constants of different metals in DMF solution of L^a

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  Cation	Quenching constant/ (L•mol-1)
  K+	0.424
  Ag+	-0.323
  Ba2+	0.071
  Co2+	1.099
  Cu2+	2.779
  Mg2+	0.899
  Pb2+	-0.011
  Fe3+	7.111×104
  Na+	0.071
  Ca2+	-0.471
  Sr2+	-0.212
  Cr2+	2.000
  Ni2+	2.036
  Cd2+	-1.519
  Zr4+	-2.904
  a L: 2.9 mL, 1×10-3 mol/L; b Concentration of metal ions: 0.1 mL, 1×10-1 mol/L; λex=365 nm.

  Figure 6

  

  Figure 6.  Effect of the disturbing metal ions on Fluorescence recognition of L to Fe³⁺

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  2.1.2   Zr⁴⁺ ion detection

  Compared with Fe³⁺ ion, Zr⁴⁺ ion exhibits superior fluorescence enhancement effect on L. To explore the detection effects of L in DMF (2.9 mL, 1×10^-6 mol•L^-1) as the fluorescence probe of Zr⁴⁺, concentration-dependent experiments were further taken (Figure 7). The fluorescence intensity of L gradually enhanced with the increasing concentration of Zr⁴⁺ ion. The fluorescence enhancement may be attributed to the formation of Zr-O and Zr-N bonds in L and Zr⁴⁺ ions, which enhance the rigid structure of the complexes. Simultaneously, the transition from n-π* to π-π* in the complexes may also be the reason of fluorescence enhancement. The Job's curve was given according to the fluorescence concentration curve of L and Zr⁴⁺ions (Figure 7b). The results showed that the molar fraction of [Zr⁴⁺]/[L+Zr⁴⁺] was 0.5 when the curve has inflection point, demonstrating 1: 1 binding stoichiometry ration for L+Zr⁴⁺. Moreover, to evaluate the detection effects of L to Zr⁴⁺ ion, the fluorescence spectra of L in DMF (2.9 mL, 1×10^-5 mol•L^-1) with different concentrations of Zr⁴⁺ ion were taken (Figure 8). The experimental results show that with the addition of different concentrations Zr⁴⁺ ion, the fluorescence intensity of L gradually enhanced and showed a highly broad linear relationship with the concentration of Zr⁴⁺ ion from 1×10^-5 to 1× 10^-4 mol•L^-1 expressed as an equation of y=3.592× 10⁶x+39.24337 and R=0.99437, where y is fluorescence intensity of L with different concentration Zr⁴⁺ and x is the concentration of Zr⁴⁺ ion. According to the fluorescence intensity of L, different concentration of Zr⁴⁺ and benesi-Hildebrand equation, the detection limit of Zr⁴⁺ in L solution is calculated to be 3.60×10^-6 mol/L.

  Figure 7

  

  Figure 7.  (a) Fluorescence spectra of L with different concentration Zr⁴⁺ and (b) Job's plot of L with Zr⁴⁺ (λ_ex=300 nm)

  (a) [L]=2.9 mL, 1×10^-5 mol•L^-1; [Zr⁴⁺]=0.1 mL, 1×10^-6~10×10^-6 mol•L^-1. (b) Complexation ratio of L and Zr⁴⁺, [Zr⁴⁺]=0.1 mL, 1× 10^-6~10×10^-6 mol•L^-1

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  Figure 8

  

  Figure 8.  (a) Fluorescence spectra of L with different concentration Zr⁴⁺ and (b) detection limit of L with Zr⁴⁺ (λ_ex=348 nm)

  (a) [L]=2.9 mL, 1×10^-5 mol•L^-1; [Zr⁴⁺]=0.1 mL, 1×10^-5~10×10^-5 mol• L^-1. (b) Detection limit of Zr⁴⁺; [Zr⁴⁺]=0.1 mL, 1×10^-5~10× 10^-5 mol•L^-1

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  Of course, the antiinterference ability is also very important for sensors, so a series of antijamming experiments were performed for L (Figure 9). Initially, the fluorescence intensity of L containing Zr⁴⁺ ion shows negligible change with the addition of other metal ions except Cr²⁺ ion. The negligible change of the fluorescence intensity indicates that L can detect Zr⁴⁺ ion in the presence of other metal ions (Co²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Ag⁺, Sr²⁺, Ba²⁺, Ca²⁺, Na⁺, K⁺, Cd²⁺, Mg²⁺).

  Figure 9

  

  Figure 9.  Effect of the disturbing metal ions on Fluorescence recognition of L to Zr⁴⁺

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  2.2   Acetone detection

  The solvents play an important role in the fluorescence of compound L. Different organic solvents have different effects on the fluorescence of compound L. The fourteen different organic solvents, DMF, acetone (CP), xylene (XY), acetonitrile (ACN), ethyl acetate (EAC), isopropyl alcohol (IPA), dichloromethane (MC), benzene (Benzol), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), cyclohexane (CYC), 1, 4-dioxane (Diox), methanol (MT) and ethanol (EA), in DMF solution were investigated and obtained experimental data finally (Figure 10). The solvents Diox, MT and EA have enhanced fluorescence effect on compound L, and the intensity exceeds the upper limit of instrument detection. Compared with DMF, it may be due to the strong polarity and weak p-π conjugation of 1, 4- dioxane, which lead to the fluorescence enhancement and blue shift of L, while the fluorescence enhancement and red shift of L may be due to the strong polarity of methanol and ethanol, forming hydrogen bond with L. The results show that the initial fluorescence intensity of L (1×10^-5 mol•L^-1) was decreased by 94.48% when only 0.1 mL of acetone was added. The acetone showed a strong quenching effect on fluorescence of compound L. It may be that there is energy transfer between compound L and acetone, which makes the excitation of compound L and the absorption of acetone has some competitive effect, which leads to the rapid decrease of fluorescence intensity of L. It was subsequently studied a possible interference of various organic solvents on selective quenching of the fluorescence of L caused by acetone (Figure 11). It is found that there is no significant impact of other solvent on the quenching of the fluorescence caused by the presence of acetone. Interestingly, when the λ_ex is larger than 300 nm, the fluorescence quenching of compound L by acetone is not obvious. To some extent, the fluorescence effect of solvent on compound L depends on the specific λ_ex.

  Figure 10

  

  Figure 10.  Fluorescence effect of organic solvent on L (λ_ex=300 nm)

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  Figure 11

  

  Figure 11.  Interference experiment of organic solvent to L fluorescence (λ_ex=270 nm)

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  2.3   Application to the determination of Fe³⁺ in urine and water samples

  The high selectivity and sensitivity make L promising as a fluorescent probe for detecting Fe³⁺ in aqueous solution. To show its potential for application in biological samples, the fluorescent L probe was applied to the detection of Fe³⁺ in human urine samples. Six human urine samples were donated by healthy volunteers. The urine samples were acidified with nitric acid and centrifuged at 5000 r/min for 10 min. Add 0.1 mL of urine directly to DMF solution of compound L without any other treatment before test analysis. The concentrations of Fe³⁺ ions in urine were calculated by Stern-Volmer (SV) equation and the values of y=41790.2576x+0.0406 were shown in Table 2. The range of Fe³⁺ ions in six urine samples was about 1.68~5.78 μmol•L^-1 by calculation. In a sense, compound L can be used as a fluorescence probe to measure the molarity of Fe³⁺ ion conveniently. Of course, the flow injection ICPMS (inductively coupled plasma mass spectrometry) method can also be used to accurately analyze Fe³⁺ in human urine.

  Table 2

  

  Table 2.  Detection of Fe³⁺ ion concentration in human urine by fluorescence of compound L^a

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  Urine	F0	F	[Fe3+]/(μmol•L-1)		Error
  			F0/Fb	Yc
  1	573.90	411.89	5.53	5.78	±0.25
  2	573.90	449.90	3.86	4.19	±0.33
  3	573.90	505.17	1.91	1.89	±0.02
  4	573.90	510.28	1.75	1.68	±0.07
  5	573.90	435.67	4.46	4.79	±0.33
  6	573.90	475.64	2.91	3.12	±0.21
  a L: 2.9 mL, 1×10-5 mol/L; sample: 0.1 mL; λex=300 nm. b F0/F=1+KSV [Fe3+]; c y=41790.2576x+0.0406.

  Besides, the tap-water and drinking-water were also tested by the above detection methods, and the concentrations of Fe³⁺ ions were 10.7 (9.38) and 2.28 (2.36) μmol• L^-1, respectively. It should be mentioned that the Environmental Protection Ministry (P. R. China) established the standard (5.4 μmol•L^-1) for the presence of Fe³⁺ ions in drinking H₂O. In this way, the tap-water cannot meet the drinking requirements, while the direct-drinking water is within the scope of national standards.

  3.   Conclusions

  In summary, as a fluorescence probe, L shows high sensitivity and selectivity for Zr⁴⁺, Fe³⁺ ions and acetone, and the detection of Fe³⁺ ion can be observed by naked eye. Meanwhile, the experimental results show that the trace of Fe³⁺ ion could remarkably decrease the fluorescence of L. In contrast to this, the trace of Zr⁴⁺ ion could remarkably increase the fluorescence of L. The detection of Fe³⁺ ion in human urine and water was realized above two detection methods. Therefore, It is expected that the compound L can be used as a tunable organic fluorescence material by Fe³⁺ and Zr⁴⁺ ions, and also as a good probe to identify acetone in organic solvent. This study might also provide a new idea of designing fluorescent organic compound chemosensors for the sensitive and selective detection of metal ions and acetone.

  4.   Experimental section

  4.1   General methods

  All reagents were purchased commercially and used without further purification unless otherwise noted. ¹H NMR spectra were recorded using 500 MHz, and ¹³C NMR spectra were recorded using 125 MHz. Elemental analyses of C, H, N in the solid samples were tested on a Vario EL analyzer (Elementar Analysensysteme GmbH). FT-IR spectra were recorded in the range of 500~4000 cm^-1 on a Perkin-Elmer FTIR spectrometer using KBr pellets. The fluorescence spectra were acquired on an F4500 spectrometer with a 850W Xenon lamp as the excitation source at room temperature.

  4.2   Synthesis of 2, 2', 2''-(1, 3, 5-triazine-2, 4, 6-triimi- no)tribenzoic acid (L)

  The L was synthesized according to the literature method^[41~43] with some modification (Scheme 1). Generally speaking, the reaction of cyanuric chloride is step-by-step. Low temperature is conducive to the first substitution, the second substitution at 50~60 ℃, and the third substitution at 110~120 ℃. It is verified by the following two methods. The results show that they are both suitable for the synthesis of L by step-by-step and one pot reaction.

  Scheme 1

  

  Scheme 1.  Synthetic route of L

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  Method 1: 2.263 g (16.5 mmol) of 2-aminobenzoic acid and 25 mL of AcOH were added to a 100 mL round bottom flask. 0.922 g (5.0 mmol) of cyanuric chloride was dissolved in 20 mL of AcOH and slowly dripped into the round bottom flask under the ice bath. The mixture reacts at 0 ℃ for 5 h. Then, the reaction continued for 5 h at 50 ℃. Finally, the reaction refluxed at 120 ℃ for 20 min. The suspension was filtered and the product was washed several times with boiling water and ethanol, and then the product was dried in vacuum dryer at 80 ℃ for one day. 2.345 g of white powder was collected in 96.4% yield.

  Method 2: 0.922 g (5.0 mmol) of cyanuric chloride and 2.263 g (16.5 mmol) of 2-aminobenzoic acid were dissolved in 50 mL of AcOH in a 100 mL round-bottom flask. The mixture was stirred and refluxed immediately at 120 ℃ for 15 min, generating a pink aqueous suspension. Then, the suspension was filtered and the product was washed several times with boiling water and ethanol, and then the mixture was dried in vacuum dryer at 80 ℃ for one day. 2.352 g of white powder was collected in 96.7% yield.

  2, 2', 2''-(1, 3, 5-Triazine-2, 4, 6-triimino)tribenzoic acid (L): m.p.≥330 ℃ (dec.); ¹H NMR (DMF-d₇, 500 MHz) δ: 11.19 (s, 3H, COOH), 8.86 (d, J=10.0 Hz, 3H, ArH), 8.13~8.15 (m, 3H, ArH), 7.68~7.72 (m, 3H, ArH), 7.16~7.20 (m, 3H, ArH); IR (KBr) v: 3440, 3312, 1685, 1610, 1567, 1523, 1413, 1161; ¹³C NMR (DMF-d₇, 125 MHz) δ: 170.1, 164.5, 142.2, 133.8, 131.5, 121.6, 120.9, 123.3, 116.3 cm^-1. Anal. calcd for C₂₄H₁₈N₆O₆: C 59.26, H 3.73, N 17.28; found C 58.31, H 3.58, N 16.57.

  
  
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  Figure 1  Structure and fluorescent of L

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  Figure 2  Fluorescence spectra of L (2.9 mL, 1×10^-5 mol•L^-1) with different metal cations (0.1 mL, 10^-1 mol•L^-1) (λ_ex=365 nm)

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  Figure 3  (a) UV-vis spectra of L with different concentration Fe³⁺ and (b) Job's plot of L with Fe³⁺

  (a) [L]=2.9 mL, 1×10^-5 mol•L^-1; [Fe³⁺]=0.1 mL, 1×10^-6~10×10^-5 mol•L^-1. (b) complexation ratio of L and Fe³⁺, [Fe³⁺]=0.1 mL, 1× 10^-6~10×10^-5 mol•L^-1

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  Figure 4  Fluorescence spectra (a) of L with different concentration Fe³⁺ and detection limit (b) of L with Fe³⁺ (λ_ex=324 nm)

  (a) [L]=2.9 mL, 1×10^-5 mol•L^-1; [Fe³⁺]=0.1 mL, 1×10^-6~10×10^-6 mol• L^-1; (b) Detection limit of Fe³⁺, [Fe³⁺]=0.1 mL, 1×10^-6~10× 10^-6 mol•L^-1

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  Figure 5  Photograph of L containing different concentrations of Fe³⁺ ion

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  Figure 6  Effect of the disturbing metal ions on Fluorescence recognition of L to Fe³⁺

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  Figure 7  (a) Fluorescence spectra of L with different concentration Zr⁴⁺ and (b) Job's plot of L with Zr⁴⁺ (λ_ex=300 nm)

  (a) [L]=2.9 mL, 1×10^-5 mol•L^-1; [Zr⁴⁺]=0.1 mL, 1×10^-6~10×10^-6 mol•L^-1. (b) Complexation ratio of L and Zr⁴⁺, [Zr⁴⁺]=0.1 mL, 1× 10^-6~10×10^-6 mol•L^-1

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  Figure 8  (a) Fluorescence spectra of L with different concentration Zr⁴⁺ and (b) detection limit of L with Zr⁴⁺ (λ_ex=348 nm)

  (a) [L]=2.9 mL, 1×10^-5 mol•L^-1; [Zr⁴⁺]=0.1 mL, 1×10^-5~10×10^-5 mol• L^-1. (b) Detection limit of Zr⁴⁺; [Zr⁴⁺]=0.1 mL, 1×10^-5~10× 10^-5 mol•L^-1

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  Figure 9  Effect of the disturbing metal ions on Fluorescence recognition of L to Zr⁴⁺

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  Figure 10  Fluorescence effect of organic solvent on L (λ_ex=300 nm)

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  Figure 11  Interference experiment of organic solvent to L fluorescence (λ_ex=270 nm)

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  Scheme 1  Synthetic route of L

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  Table 1.  Quenching constants of different metals in DMF solution of L^a

  Cation	Quenching constant/ (L•mol-1)
  K+	0.424
  Ag+	-0.323
  Ba2+	0.071
  Co2+	1.099
  Cu2+	2.779
  Mg2+	0.899
  Pb2+	-0.011
  Fe3+	7.111×104
  Na+	0.071
  Ca2+	-0.471
  Sr2+	-0.212
  Cr2+	2.000
  Ni2+	2.036
  Cd2+	-1.519
  Zr4+	-2.904
  a L: 2.9 mL, 1×10-3 mol/L; b Concentration of metal ions: 0.1 mL, 1×10-1 mol/L; λex=365 nm.

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  Table 2.  Detection of Fe³⁺ ion concentration in human urine by fluorescence of compound L^a

  Urine	F0	F	[Fe3+]/(μmol•L-1)		Error
  			F0/Fb	Yc
  1	573.90	411.89	5.53	5.78	±0.25
  2	573.90	449.90	3.86	4.19	±0.33
  3	573.90	505.17	1.91	1.89	±0.02
  4	573.90	510.28	1.75	1.68	±0.07
  5	573.90	435.67	4.46	4.79	±0.33
  6	573.90	475.64	2.91	3.12	±0.21
  a L: 2.9 mL, 1×10-5 mol/L; sample: 0.1 mL; λex=300 nm. b F0/F=1+KSV [Fe3+]; c y=41790.2576x+0.0406.

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