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. 2021 Feb 25;26(5):1233.
doi: 10.3390/molecules26051233.

A Simple Turn-off Schiff Base Fluorescent Sensor for Copper (II) Ion and Its Application in Water Analysis

Xing Zhang  1 , Ling-Yi Shen  2 , Qi-Long Zhang  1   2 , Xian-Jiong Yang  2 , Ya-Li Huang  2 , Carl Redshaw  3 , Hong Xu  1   2
Affiliations

A Simple Turn-off Schiff Base Fluorescent Sensor for Copper (II) Ion and Its Application in Water Analysis

Xing Zhang et al. Molecules. .

Abstract

An aniline-functionalized naphthalene dialdehyde Schiff base fluorescent probe L with aggregation-induced enhanced emission (AIEE) characteristics was synthesized via a simple one-step condensation reaction and exhibited excellent sensitivity and selectivity towards copper(II) ions in aqueous media with a fluorescence " turn-off " phenomenon. The detection limit of the probe is 1.64 × 10-8 mol·L-1. Furthermore, according to the results of the UV-vis/fluorescence titrations, Job's plot method and 1H-NMR titrations, a 1:2 stoichiometry was identified. The binding constant between L and Cu2+ was calculated to be Ka = 1.222 × 103. In addition, the AIEE fluorescent probe L could be applied to detection in real water samples with satisfactory recoveries in the range 99.10-102.90% in lake water and 98.49-102.37% in tap water.

Keywords: AIEE; copper(II) ion; fluorescent probe; synthesis; water detection.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Synthetic route to Schiff-base L.
Figure 1
Figure 1
(A) Fluorescence spectra of L (40 μM) in tetrahydrofuran (THF)/water mixtures with different water fractions (λex/λem = 428 nm/565 nm, slit: 5/5 nm, voltage: 660 v). (B) Plots of fluorescence intensity at 565 nm. (C) photographs in THF/water mixtures with different water fractions taken under 365 nm UV irradiation.
Figure 2
Figure 2
The fluorescence intensity stability of the L and L-Cu2+ systems versus different (A) pH values and (B) reaction time.
Figure 3
Figure 3
(A) The UV–vis and (B) Fluorescence spectra of the fluorescence probe L interacting with different metal ions (λex/λem = 428/565 nm, slit: 5/5 nm, voltage: 900 v).
Figure 4
Figure 4
Bar diagram of the competitive experiments of various metal cations (A) and anions (B) on the fluorescence intensity of the probe/Cu2+ complex in buffer solution.
Figure 5
Figure 5
(A) Fluorescence spectra on addition of Cu2+ to the probe; (B) Job’s plot for the determination of the stoichiometry of L and Cu2+ in the mixture of THF/H2O (VTHF:VH2O = 4/1), the total concentration of L and Cu2+ was 40 μM.
Figure 6
Figure 6
The Benesi–Hildebrand plot of 1/(F − F0) versus 1/[Cu2+].
Figure 7
Figure 7
1H-NMR spectroscopic titration spectra of L-Cu2+ on increasing concentrations of Cu2+ in d-DMSO/D2O solution.
Figure 8
Figure 8
The X-ray single crystal diffraction image of probe L (Dashed lines represent hydrogen bonds, Symmetry code:# = −x, 1 − y, 1 − z).
Figure 9
Figure 9
The possible recognition mechanism process for detection of copper ions.
See this image and copyright information in PMC

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