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A new efficient Schiff base sensor SB3 for fluorescent and colorimetric "naked-eye" "turn-on" sensing of cyanide anion (CN - ) with excellent sensitivity and selectivity was developed. The 4,4'-(perfluoropropane-2,2-diyl)bisphenol group and two phenyl groups were covalently linked by two C = N bonds to extend the conjugation length. The four hydroxyl groups can improve the water solubility of the SB3 sensor. The SB3 sensor exhibited high specificity towards CN - by interrupting its intramolecular charge transfer, resulting in a color change and remarkable "turn-on" green fluorescence emission. The sensing mechanism is caused by the nucleophilic addition of CN- toward imine groups of the SB3 sensor, leading to breaks of the conjugation, fluorescent spectral changes, and color change. It was confirmed by 1 H NMR titration and Mass spectra. The detection limits for CN - and Al 3+ obtained by fluorescence spectrum are 0.80 µM and 0.25 µM, respectively. The SB3 sensor can act as an efficient chemical sensor for detecting the CN - and Al 3+ ions under common environmental and physiological conditions (pH 5-12). Besides, the sensor can also detect CN - in food materials (such as sprouting potatoes and cassava flour) and imaging CN - in living cells with strong "turn-on" fluorescence at 490 nm. SB3 is an excellent CN - sensor that exhibits some advantages, including easy synthesis, distinct fluorescence and color change, high selectivity, low detection limit, and good anti-interference ability to analyze solution and food samples, together with fluorescence cell imaging., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

[Display omitted] • A nickel complex (NiC) sensor with thiourea binding sites was developed for colorimetric sensing. • The detection limits of NiC toward CN− and S2– reached 3.54 × 10−8 and 2.87 × 10−8 M. • The interaction between NiC and analytes (CN– or S2–) results from deprotonation. • The colorimetric response is due to the intramolecular charge transfer mechanism. • NiC sensor was applied to detect CN− in the food samples. Since cyanide is highly toxic that can lead to respiratory arrest and death, it is important to develop practical diagnostic methods for the sensing of cyanide. In this study, the colorimetric sensing of cyanide was achieved by a nickel complex (NiC) sensor with thiourea binding sites. NiC was prepared and characterized by 1H NMR, single-crystal X-ray crystallography, FTIR, and Mass spectra. When the cyanide and sulfide ions were added to NiC sensor, the color changed from light yellow to canary yellow and pale yellow to golden yellow, respectively. NMR titration results confirmed that the colorimetric response toward cyanide resulted from the deprotonation and formation of a guest–host complex. A binding mechanism is proposed based on the mass spectra, 1H NMR titration, and stoichiometry studies. The binding constant and detection limit of the NiC sensor toward cyanide was also investigated. The detection limits of NiC toward cyanide and sulfide reached 35.4 nM and 28.7 nM, respectively, lower than the World Health Organization (WHO)-allowed cyanide concentration in drinking water. The NiC complex possesses high selectivity to cyanide and sulfide through deprotonation of the –NH- protons. The detection of trace amounts of cyanide ions in natural food samples, such as cassava flour and sprouting potatoes, was also achieved by the NiC sensor. [ABSTRACT FROM AUTHOR]