A 1-Hydroxy-2,4-Diformylnaphthalene-Based Fluorescent Probe and Its Detection of Sulfites/Bisulfite

Abstract

A novel 1-hydroxy-2,4-diformylnaphthalene-based fluorescent probe L was synthesized by a Knoevenagel reaction and exhibited excellent sensitivity and selectivity towards sulfite ions (SO₃^2-) and bisulfite ions (HSO₃^-). The detection limits of the probe L were 0.24 μM using UV-Vis spectroscopy and 9.93 nM using fluorescence spectroscopy, respectively. Furthermore, the fluorescent probe L could be utilized for detection in real water samples with satisfactory recoveries in the range 99.20%~104.30% in lake water and 100.00%~104.80% in tap water by UV-Vis absorption spectrometry, and in the range 100.50%~108.60% in lake water and 102.70%~103.80% in tap water by fluorescence spectrophotometry.

Keywords: crystal structure; fluorescent probe; real sample detection; sulfite/bisulfite.

Scheme 1

Synthetic route to probe L.

Figure 1

(A) The UV-Vis and (B) fluorescence spectra of the fluorescence probe L (15 μM) in EtOH/water mixtures with different water fractions (λ_ex/λ_em = 576 nm/605 nm, slit: 5/5 nm, voltage: 800 v). (C) Photographs in EtOH/water mixtures with different water fractions taken under 365 nm UV irradiation. Inset of (B): Plots of fluorescence intensity at 605 nm.

Figure 2

(A) The UV-Vis and (B) Fluorescence spectra of the fluorescence probe L (15 μM) in EtOH/water (V_EtOH/V_water = 2/3) at different pH values (λ_ex/λ_em = 576 nm/605 nm, slit: 5/5 nm, voltage: 800 v). Inset: (A) Effect of different pH values on the absorbance of probe L at 550 nm. (B) Influence of pH values on fluorescence probe L at 605 nm.

Figure 3

(A) The UV-Vis and (B) fluorescence spectra of the fluorescence probe L (15 μM) in EtOH/water (V_EtOH/V_water = 2/3) with the addition of SO₃²⁻/HSO₃⁻ (750 μM) at different pH values (λ_ex/λ_em = 576 nm/605 nm, slit: 5/5 nm, voltage: 600 v). Inset: (A) Effect of different pH values on the absorbance of probe L with the addition of SO₃²⁻/HSO₃⁻ at 550 nm. (B) Influence of pH values on fluorescence probe L with the addition of SO₃²⁻/HSO₃⁻ at 605 nm.

Figure 4

(A) The UV-Vis and (B) fluorescence spectra of the fluorescence probe L interacting with different anions and small amino-containing molecules (λ_ex/λ_em = 576/605 nm, slit: 5/5 nm, voltage: 600 v).

Figure 5

Bar diagram of the competitive experiments of various anions and small amino-containing molecules on the absorbance (A) and fluorescence intensity (B) of the probe/SO₃²⁻/HSO₃⁻ complex in buffer solution.

Figure 6

Bar diagram of the competitive experiments of various metal cations on the absorbance (A) and fluorescence intensity (B) of the probe/SO₃²⁻/HSO₃⁻ complex in buffer solution.

Figure 7

(A) UV-Vis absorption spectra on the addition of SO₃²⁻/HSO₃⁻ to the probe; (B) linear curve of absorbance of probe solution at 550 nm and concentration of SO₃²⁻/HSO₃⁻ (30 μM–300 μM). Inset: Curve of absorbance at 550 nm with different concentrations of SO₃²⁻/HSO₃⁻; photograph of the solutions under illumination with sunlight showing the change in the solution after the titration is complete.

Figure 8

(A) Fluorescence spectra on addition of SO₃²⁻/HSO₃⁻ to the probe; (B) linear curve of fluorescence intensity of probe solution at λ_{max em} = 605 nm and concentration of SO₃²⁻/HSO₃⁻ (15 μM–300 μM). Inset: Curve of fluorescence intensity at λ_{max em} = 605 nm with different concentrations of SO₃²⁻/HSO₃⁻; photograph of the fluorescence change under the irradiation of 365 nm UV lamp after the titration is complete.

Figure 9

The single crystal X-ray diffraction image of probe L.

Figure 10

Proposed sensing mechanism of probe L for SO₃²⁻/HSO₃⁻.

Figure 11

High resolution mass spectra (HRMS) of the reaction product of probe L upon the addition of SO₃²⁻/HSO₃⁻.