Highly Sensitive Ratiometric Fluorescent Paper Sensors for the

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Article Cite This: ACS Omega 2019, 4, 4918−4926

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Highly Sensitive Ratiometric Fluorescent Paper Sensors for the Detection of Fluoride Ions Xiaoming Wu, Hao Wang, Shaoxiang Yang,* Hongyu Tian, Yongguo Liu, and Baoguo Sun Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Key Laboratory of Flavor Chemistry, Beijing Technology and Business University, No. 11 Fucheng Road, Haidian District, Beijing 100048, People’s Republic of China

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S Supporting Information *

ABSTRACT: Two sensitive and ratiometric fluorescent probes (probe I and probe II) were developed for the detection of fluoride ions. Probe I can detect fluoride ions quantitatively within a range of 0−6 μM and a detection limit of 73 nM, while probe II has a range of 0−40 μM and a detection limit of 138 nM. The test strips from probe I are quickly able to recognize F− (5 min) inside of the F− safety level in drinking water (1.0 mg/L, ∼5 μM) under 254 nm ultraviolet light, and the test strips from probe II quickly recognize F− (12 min) in dangerously high F− levels in water (4.0 mg/L, ∼21 μM) under 254 nm ultraviolet light. This combination of fluorescent paper sensors from probe I and probe II can be used as a simple and convenient tool to determine whether water is safe to drink or dangerous.

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acid−base interactions, 32−34 hydrogen-bonding interactions,35−37 and the F−-induced fracture of Si−O, Si−C, and P−O bonds.38−44 The F− ratiometric fluorescent probe based on a F−-induced bond-breaking mechanism is still relatively uncommon.45−47 As a fluorescent probe with a F−-induced bond-breaking mechanism is highly selective and sensitive, ratiometric fluorescent probes can reduce interference from environmental conditions, instrumental efficiency, excitation intensity, and concentration. In this work, two F− ratiometric fluorescent probes were developed for the sensitive detection of F− based on the Si−O bond cleavage. The two probes were prepared with naphthalene−benzothiazole as the fluorophore, tert-butyldimethylsilyl (probe I) and tert-butyldiphenylsilyl (probe II) as the reactive groups, and the Si−O bond as the reaction site. The two probes have a high sensitivity and selectivity to F−. The two probes could be used for the quantitative detection of F− in water. In addition, the luminescence of probe I test paper will enhance the F− safety level in drinking water (1 mg/L, ∼5 μM) under a 254 nm ultraviolet light. When the F− content surpasses dangerously high levels (4 mg/L, ∼21 μM), the luminescence of probe II test paper will enhance under a 254 nm ultraviolet light. The fluorescent paper sensors can be used as a simple and convenient tool to check the fluoride ion content in water, determining whether the water meets drinking standards.

INTRODUCTION The fluoride anion (F−) is an important trace element in the human body.1 It carries both benefits and dangersa low concentration of F− can be effective in treating osteoporosis and the prevention of caries, but excess fluoride will cause dental and skeletal fluorosis, as well as urolithiasis and kidney and gastric disorders.2,3 F− is primarily obtained from food and drinking water. Most countries set strict limits on F− that is the permitted level of fluorine in foods.4 In China, these limits are as follows: in eggs and vegetables ≤1.0 mg/kg, fruit ≤0.5 mg/kg, and in meat and freshwater fish ≤2.0 mg/kg.5 Low F− levels (0.5−1.5 mg/L) in drinking water helps to strengthen bones and prevent dental caries, and the permitted level of F− in drinking water in China lies at ≤ 1.0 mg/L.6 The content of F− in natural water is 0.3−0.5 mg/L and can reach 2.0−5.0 mg/L in groundwater with fluorine ore deposits.7,8 Over 2.0 mg/L of F− in drinking water can cause damage to kidney and liver functions and over 4 mg/L will deform human bones and cause fluorosis.9,10 As a result, developing a simple new, sensitive and quick method for detecting F− concentrations is of great importance.11 To date, several methods have been developed for the detection of F−, including fluorine reagent colorimetry,12,19 F NMR,13 ion chromatography,14 and the ion-selective electrode.15 However, most approaches dedicated to determining F− levels are complicated, time-consuming, and expensive procedures that have limited adaptability.16,17 Recently, fluorescent probes have been highly sensitive, operationally simple, and quick in the determination of F− in water, food, cells, and mammals.18−25 Many F− fluorescent probes have been reported whereby the reaction mechanisms are based on anion−π interactions,26,27 competitive interactions,28−31 Lewis © 2019 American Chemical Society

Received: January 31, 2019 Accepted: February 19, 2019 Published: March 5, 2019 4918

DOI: 10.1021/acsomega.9b00283 ACS Omega 2019, 4, 4918−4926

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Scheme 1. Synthesis of Probe I and Probe II

Figure 1. (a) Fluorescent spectra of probe I (10 μM) in different buffer solutions (pH, 3−12) with DMSO (v/v = 3:1) at 25 °C; (b) fluorescent spectra of probe I (10 μM) added to F− (300 μM) in different buffer solutions (pH, 3−12) with DMSO (v/v = 3:1) at 25 °C; (c) fluorescent spectra of probe II (10 μM) in different buffer solutions (pH, 3−12) with DMSO (v/v = 3:1) at 25 °C; (d) fluorescent spectra of probe II (10 μM) added to F− (300 μM) in different buffer solutions (pH, 3−12) with DMSO (v/v = 3:1) at 25 °C; (e) fluorescent spectra of probe I (10 μM) added to F− (300 μM) in different solvents (CH3CN, DMSO, and C2H5OH) with H2O (v/v = 3:1); (f) fluorescent spectra of probe II (10 μM) added to F− (300 μM) in different solvents (CH3CN, DMSO, and C2H5OH) with H2O (v/v = 3:1).

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RESULTS AND DISCUSSION

(Figures S1−S6, Supporting Information). They are all general operations for organic synthesis. Sensing Properties of Probes toward Fluoride Anions. First, the influences of pH and different solvents on the fluorescence performance of probes I and II were investigated. The pH response of the probes (10 μM) to F− (300 μM) was evaluated in different buffers (pH 3.0, 4.0, 5.0, 6.0, 7.0, 7.4, 8.0, 9.0, 10.0, 11.0, and 12.0) with dimethyl sulfoxide (DMSO, v/v =

Probe Synthesis. Probes I and II were prepared in a onestep reaction (Scheme 1) using the nucleophile substitution reaction of 6-hydroxy-2-naphthaldehyde (compound 1) with chlorosilane (compound 2). The reaction mixture was then purified using column chromatography to produce probes I and II; 1H NMR, 13C NMR, and HRMS were used for confirmation 4919


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Figure 2. (a) Fluorescence spectra of probe I (10 μM) with F− (0, 2, 4, 6, 8, 10, 20, 40, and 60 μM); (b) photograph of probe I solutions (10 μM) subjected to F− (0, 2, 4, 6, 8, and 10 μM) under ambient light and 365 nm UV light; (c) fluorescence spectra of probe II (10 μM) with F− (0, 5, 10, 15, 20, 25, 30, 35, 50, 60, 70, 80, 90, and 100 μM); (d) photograph of probe II solutions (10 μM) subjected to F− (0, 10, 15, 20, 25, and 30 μM) under ambient light and 365 nm UV light; (e) time-dependent fluorescence spectra of probe I (10 μM) in the presence of F− (3 μM) in DMSO with H2O (v/ v, 3:1) at 25 °C. Tests were performed in triplicate; (f) time-dependent fluorescence spectra of probe II (10 μM) in the presence of F− (20 μM) in DMSO with H2O (v/v, 3:1) at 25 °C. Tests were performed in triplicate.

3:1) at 25 °C. The fluorescent intensity of probe I exhibited irregular change (Figure 1a), and as F− was added, the fluorescent intensity of probe I did not obviously change (Figure 1b). With an increase in pH from 3 to 12, the fluorescent intensity of probe II at 416 nm decreased, but increased at 487 nm (Figure 1c). The fluorescence emission ratio (F416nm/F487nm) of probe II has a linear relation with different buffers from pH 7.0 to 10.0 (Figure S7, Supporting Information), but as F− was added, the fluorescent intensity of probe II did not seem to change and exhibited irregular change (Figure 1d). They are almost the same between the fluorescent intensity of probe II and probe II-F−. It showed that probe II could not identify the F− in these condition. The solvent response of probe I (10 μM) to F− (300 μM) was evaluated in different solvents (CH3CN, DMSO, and C2H5OH) with H2O (v/v = 3:1) (Figure 1e). The fluorescent intensity of probe I and probe I-F− were almost the same in CH3CN and C2H5OH. The greatest difference in fluorescent intensity between probe I and probe I-F− occurred in DMSO with H2O (v/v = 3:1). After the F− was added, the fluorescent intensity decreased rapidly and two fluorescence emission peaks emerged

at 425 and 503 nm. The same phenomenon occurred with probe II (10 μM)the greatest testing solvent was DMSO with H2O (v/v = 3:1). As F− was added, two fluorescence emission peaks appeared at 416 and 487 nm (Figure 1f). Therefore, DMSO with H2O (v/v = 3:1) was chosen as the testing solvent in the following work. The relationship between the fluorescent intensity of probe I and F− concentration was investigated next. As different concentrations of F− (0, 2, 4, 6, 8, 10, 20, 40, and 60 μM) were added, the fluorescent intensity at 406 nm decreased, whereas it increased at 512 nm (Figure 2a). Probe I was a ratiometric fluorescent probe. As the concentrations of F− increased (0, 2, 4, 6, 8, and 10 μM), the luminescent intensity gradually enhanced and could be observed with the naked eye under 365 nm ultraviolet light (Figure 2b). Probe II was also a ratiometric fluorescent probe. As different concentrations of F− (0, 5, 10, 15, 20, 25, 30, 35, 50, 60, 70, 80, 90, and 100 μM) were added, the fluorescent intensity decreased at 401 nm but increased at 510 nm (Figure 2c). The luminescent intensity of probe II gradually enhanced after different concentrations of F− (0, 10, 15, 20, 25, and 30 μM) were added. This could also be 4920


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Figure 3. (a) Fluorescence spectra of probe I (10 μM) with F− (0, 1, 2, 3, 4, 5, and 6 μM); (b) plot of fluorescence intensity of probe I differences with F− ranging from 0 to 6 μM; (c) fluorescence spectra of probe II (10 μM) with F− (0, 5, 10, 15, 20, 25, 30, and 35 μM); (d) plot of fluorescence intensity of probe II differences with F− ranging from 0 to 35 μM.

Figure 4. (a) Fluorescence intensity change of probe I (10 μM) upon addition of various species (10 μM for each. 1, blank; 2, Cu2+; 3, Ca2+; 4, K+; 5, Na+; 6, Mg2+; 7, HS−; 8, HSO3−; 9, SO32−; 10, SO42−; 11, Fe2+; 12, NH4+; 13, Cl−; 14, Br−; 15, I−; 16, H2O2; 17, Cys; 18, GSH; 19, Hcy; 20, Fe3+; 21, Glu. 4 μM for F−). Tests were performed in triplicate; (b) fluorescence intensity change of probe II (10 μM) upon addition of various species (10 μM for each. 1, blank; 2, Cu2+; 3, Ca2+; 4, K+; 5, Na+; 6, Mg2+; 7, HS−; 8, HSO3−; 9, SO32−; 10, SO42−; 11, Fe2+; 12, NH4+; 13, Cl−; 14, Br−; 15, I−; 16, H2O2; 17, Cys; 18, GSH; 19, Hcy; 20, Fe3+; 21, Glu. 20 μM for F−). Tests were performed in triplicate.

a result, 25 min was the suitable reaction time for probe II toward F−. The results showed that the reaction time for probe II-F− was longer than probe I-F−, which is largely due to the groups around the silicon atom being different in steric hindrance (phenyl > methyl). When F− was gradually added (0, 1, 2, 3, 4, 5, and 6 μM), the fluorescence emission ratio (F510nm/F401nm) of probe I gradually decreased (Figure 3a). This was linear with the concentration of F− (Figure 3b; R2 = 0.9961) with a detection limit of 73 nM (S/ N = 3).18−20 The fluorescence emission ratio (F512nm/F406nm) of probe II gradually decreased as different concentrations of F− (0, 5, 10, 15, 20, 25, 30, and 35 μM) were added (Figure 3c). The fluorescence emission ratio (F512nm/F406nm) of probe I was linear

seen with the naked eye under 365 nm ultraviolet light (Figure 2d). Despite adding more F−, the luminescence of probe II was less obvious than probe I. A time-response study of the probe to F− was carried out by monitoring the fluorescence emission ratio. It was found that the fluorescence emission ratio (F512nm/F406nm) of probe I remained constant from 0 to 180 s (Figure 2e). The fluorescence emission ratio (F512nm/F406nm) of probe I-F− decreased gradually and reached an equilibrium at 120 s (2 min). Therefore, 2 min was the suitable reaction time for probe I toward F−. Meanwhile, the fluorescence emission ratio (F510nm/F401nm) of probe II remained constant from 0 to 30 min (Figure 2f). The fluorescence emission ratio (F512nm/F406nm) of probe I-F− decreased gradually and reached an equilibrium at 25 min. As 4921


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Scheme 2. Mechanism for Reaction of Probe I and Probe II with F−

Figure 5. 1H NMR titration spectra of probe I-F−.

Figure 6. HPLC spectra of probe II-F−.

with the concentration of F− (Figure 3d; R2 = 0.9952). The limit of detection was calculated to be 138 nM (S/N = 3).18−20

To investigate the selectivity of the probes for F−, various competitors including Hcy, Cys, Glu, GSH, H2O2, Cu2+, Ca2+, 4922


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Table 1. Detection of F− in Real Samples F− level found (μmol/L)

added (μmol/L)

found (μmol/L)

recovery/%

RSD/% (n = 3)

water

2.479 ± 0.190

yellow river

2.128 ± 0.205

15.00 30.00 15.00 30.00 15.00 30.00 15.00 30.00 15.00 30.00

15.49 29.718 16.364 29.876 15.95 29.677 15.769 29.677 16.266 29.58

99.78 98.95 108.9 99.49 104.2 97.92 103.79 98.1 104.59 100.33

1.657 0.342 2.176 0.366 3.160 0.751 5.057 0.622 2.993 0.703

sample

green tea

2.47 ± 0.216

mineral water

2.37 ± 0.200

milk

2.527 ± 0.252

Na+, Mg2+, K+, HSO3−, Fe2+, SO42−, HS−, Fe3+, SO32−, Cl−, NH4+, I−, and Br− were tested. None of these competitors caused a fluorescent response by probe I and probe II. In addition, a competition experiment was conducted by adding F− to probe solutions containing these competitors. The fluorescence emission ratio (F510nm/F401nm) of probe I (Figure 4a) and the emission ratio (F512nm/F406nm) of probe II (Figure 4b) were very close to those of F− alone. The results show that probe I and probe II are excellent selective tools for F− detection. Reaction Mechanism. A possible response mechanism may contribute to the nucleophile substitution reaction of the probes with F− generating compound 1, compound 3, or compound 4 (Scheme 2). The reaction mechanism of probe I with F− was first verified by 1H NMR titration. The proton signals at 8.52 ppm (a′-H), 1.25 ppm (b′-H), and 0.80 ppm (c′-H) strengthened with an increase in the concentration of F−. Also, the signals at 8.51 ppm (a-H), 0.98 ppm (c-H), and 0.25 ppm (b-H) weakened before disappearing with an increase in the concentration of F− (Figure 5). The mechanism was further confirmed by mass spectrometry (MS), where a peak at m/z = 278.49 was observed, which correlates with the formation of compound 1 (Figure S8, Supporting Information). A peak at m/ z = 133.23 correlates with the formation of compound 3 (Figure S8, Supporting Information). The reaction mechanism of probe II with F− was first verified by HPLC. As F− equivalent to 1 was added, the peak of probe II disappeared and the peak of compound 1 appeared (Figure 6). The mechanism was further confirmed by MS, where a peak at m/z = 278.49 was observed, which correlates with the formation of compound 1 (Figure S9, Supporting Information). A peak at m/z = 257.79 correlates with the formation of compound 4 (Figure S9, Supporting Information). The results suggest that the reaction mechanism of the probes with F− arose due to the nucleophile substitution reaction. The reactivity of probe I and probe II with F− would be affected by the groups around the silicon atom. As phenyl has a greater electron-donating ability and steric hindrance than methyl, it would be easy for probe I to recognize F−. Detection of F− in Real Samples. All of the above results showed that probe I and probe II had a good response to F− in complex systems. The ability of probe II to detect F− in real samples was demonstrated in order to prove its applicability. Five kinds of real samples (tap water, yellow river, mineral water, green tea, and milk; 20 μL) were added to probe II solutions (10 μM, 2.0 mL). The concentration of F− were detected in the five real samples (Table 1). Then, different amounts of F− (15 and 30 μM) were added. The recovery values from 97.92 to 104.59% show that probe II is able to detect F− in real water samples. As probe I has similar characteristics to probe II, probe I could be expected to detect concentrations of F− in real samples.

Application in Test Strips. The test strips PI-A were placed on a glass plate, and 10 μL of different concentrations of F− (0, 1, 2, 3, 4, 5, and 6 μM) were added. After 5 min, the luminescence of test strips PI-A clearly enhanced the F− safety level of drinking water (1.0 mg/L, ∼5 μM). This could be observed with the naked eye under 254 nm ultraviolet light (Figure 7a).

Figure 7. (a) Photograph of the test strips PI-A subjected to F− (0, 1, 2, 3, 4, 5, and 6 μM) under ambient light and 254 nm UV light; (b) photograph of the test strips PI-B subjected to F− (0, 1, 2, 3, 4, 5, and 6 μM) under ambient light and 254 nm UV light; (c) photograph of the test strips PII subjected to F− (0, 3, 6, 13, 21, and 27 μM) under ambient light and 254 nm UV light; (d) photograph of the test strips PII subjected to F− (0, 3, 6, 13, 21, and 27 μM) under ambient light and 365 nm UV light.

The test strips of PI-B were placed on a glass plate, and 20 μL of different concentrations of F− (0, 1, 2, 3, 4, 5, and 6 μM) were added. After 60 min, the luminescence of the test strips PI-B clearly enhanced the F− safety level of drinking water (1.0 mg/L, ∼5 μM) under 254 nm ultraviolet light (Figure 7b). The test strips of PII were placed on a glass plate, and 20 μL of different concentrations of F− (0, 3, 6, 13, 21, and 27 μM) were added. After 12 min, the luminescence of the test strips PII had obviously enhanced as the F− content exceeds dangerously high levels (4 mg/L, ∼21 μM) under 254 nm (Figure 7c) and 365 nm (Figure 7d) ultraviolet light. All these results indicate that the test strips of probe I and probe II can be used as a simple and convenient tool to check the fluoride ion content in water, determining whether the water can be drunk. Although many F− fluorescent probes have been reported (Table S1, Supporting Information), no F− fluorescent test strip probe can recognize F− in a 1.0 mg/L concentration quickly. 4923


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The fluorescent paper sensors developed in this work can be used as a simple and convenient tool to check the fluoride ion content in water, determining whether the water is of drinking standard.

134.95, 132.28, 131.16, 130.84, 129.64, 128.86, 128.62, 128.10, 127.97, 127.65, 127.12, 125.92, 124.89, 123.20, 122.79, 114.92, 27.02, and 19.15. HRMS (ESI): calcd for [M + H]+, 516.181189; found, 516.181189. Preparation of Solutions of Probes and Analytes. DMSO, as a reagent, was used to dissolve probe I, probe II, Cys, Glu, GSH, and Hcy. After mixing, a probe 1 stock solution was obtained. The analytes H2O2, Na2S, KBr, Na2SO3, FeCl3, CuSO4, NaCl, MgSO4, FeS, KI, FeS, NaHSO3, and NH4Cl were dissolved in distilled water to obtained 10 mM aqueous solutions. Various concentrations could be obtained by diluting these stock solutions with distilled water. Procedures of Fluoride Anion Determination. Preparation of the test system: 0.02 mL probe solution was added to a cuvette. Then, acetonitrile was poured into the cuvette to make up a volume of 2 mL. Finally, the ion solution was added. After waiting 5 min, it was mixed completely. Samples of the mixture were analyzed in the fluorescence spectrometer using the conditions of λex = 342 nm (probe I), λex = 338 nm (probe II); temperature = 25 °C; voltage = 500 V; and slit widths = 2.5, 2.5 nm. Preparation of Test Strips. The test strips PI-A of probe I were prepared using waterman filter paper (1 cm × 1 cm pieces). The test strips PI-A of probe I were prepared by dropping a 10 μL DMSO solution of probe I (10 μM) onto the filter paper and then baking for 5 min in an oven at 70 °C. The test strips PI-B of probe I were prepared by dropping 20 μL of the DMSO solution of probe I (10 μM) onto the filter paper and then air-drying for 10 min. The test strips PII of probe II were prepared by dropping 20 μL of the DMSO solution of probe II (10 μM) onto the filter paper and then air-drying for 5 min.

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CONCLUSIONS In summary, two ratiometric fluorescent probes (probe I and probe II) were developed for the detection of F−. The function of the probes relies on the nucleophile substitution reaction of the probes with F−, which generates 6-hydroxy-2-naphthaldehyde, as verified by 1H NMR, HPLC, and MS. The test strips of probe I quickly recognize F− (5 min) in the F− safety level in drinking water (1.0 mg/L, ∼5 μM) under 254 nm ultraviolet light, and the test strips of probe II quickly recognize F− (12 min) in the F− dangerously high levels in water (4.0 mg/L, ∼21 μM) under 254 nm ultraviolet light. The fluorescent paper sensors of probe I and probe II can be used as a simple and convenient tool to check the fluoride ion content in water, determining whether the water is safe to drink or if the water is dangerous.

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EXPERIMENTAL SECTION

Chemicals. The chemicals cysteine (Cys, 99%), 4dimethylaminopyridine (DMAP, 99%), tert-butyldimethylsilyl chloride (98%), glutathione (GSH, 98%), 2-aminothiophenol (98%), tert-butyldiphenylsilyl chloride (98%), homocysteine (Hcy, 99%), 6-hydroxy-2-naphthaldehyde (98%), glutamic acid (Glu, 99%), hydrogen peroxide (H2O2, 30%), and the analytically pure reagents sodium sulfide (Na2S), calcium chloride (CaCl2), potassium bromide (KBr), sodium sulfite (Na2SO3), ferric chloride (FeCl3), cupric sulfate (CuSO4), sodium chloride (NaCl), magnesium sulphate (MgSO4), ferrous sulfide (FeS), potassium iodide (KI), sodium hydrogen sulfite (NaHSO3), ammonium chloride (NH4Cl), DMSO, and trichloromethane (CHCl3) were purchased from Bailinwei Co., Ltd. (Beijing, China). Instruments. NMR spectra were obtained from a Bruker AV 300 MHz. HRMS spectra were obtained using a Bulu Ke Mass Spectrometer. Fluorescence spectra were obtained from a fluorescence spectrometer (Hitachi F-4600). Preparation of Probe 1. 6-Hydroxy-2-naphthaldehyde (compound 1; 0.999 g, 3.609 mmol), chlorosilane (compound 2; 0.543 g, 3.609 mmol), and DMAP (0.120 g, 1.083 mmol) were added to a flask, and 20 mL CHCl3 was then added. The mixture was stirred at 80 °C for 8 h and then cooled down to room temperature, filtered in vacuum, the filtrate was concentrated and purified by column chromatography with petroleum ether and ethyl acetate (v/v = 10:1) as the eluent to get probe I and probe II.48,49 Probe I. 1H NMR (300 MHz, CDCl3): δ (ppm) 8.54 (s, 1H), 8.15 (dd, J = 13.7, 5.1 Hz, 2H), 7.95−7.77 (m, 3H), 7.52 (t, J = 7.1 Hz, 1H), 7.40 (t, J = 7.1 Hz, 1H), 7.23 (d, J = 2.1 Hz, 1H), 7.15 (dd, J = 8.8, 2.4 Hz, 1H), 1.04 (s, 9H), and 0.28 (s, 6H). 13C NMR (75 MHz, CDCl3): δ (ppm) 167.47, 154.15, 152.94, 135.15, 133.84, 129.45, 127.85, 126.53, 125.40, 124.13, 123.78, 122.14, 121.98, 120.60, 113.96, 28.69, 28.35, 24.69, 21.68, and 17.28; HRMS (ESI): calcd for [M + H]+, 392.149888; found, 392.150166. Probe II. 1H NMR (300 MHz, CDCl3): δ (ppm) 7.70 (ddd, J = 7.3, 5.8, 3.6 Hz, 6H), 7.49−7.43 (m, 2H), 7.41−7.34 (m, 6H), 6.55 (s, 1H), 1.36−1.18 (m, 3H), 1.10 (s, 2H), and 0.95 (s, 9H). 13 C NMR (75 MHz, CDCl3): δ (ppm) 136.83, 135.87, 135.54,

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.9b00283. 1

H NMR, 13C NMR, and HRMS spectra of probe I and probe II, fluorescence intensity of probe II in different buffer solutions, MS spectra of probe I-F− and probe IIF−, and comparison of reported F− fluorescence probes (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +86-1068985382. ORCID

Shaoxiang Yang: 0000-0002-9944-7472 Hongyu Tian: 0000-0002-7117-6420 Baoguo Sun: 0000-0003-4326-8237 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

This work was supported by National key research and development program (2016YFD0400801); the Support Project of High-level Teachers in Beijing Municipal Universities in the Period of 13th Five−year Plan (CIT&TCD201804021). 4924


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ACS Omega

Article

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