Turn-on fluorescent sensor for the detection of cyanide based on a novel dicyanovinyl phenylacetylene†
*ab
Abstract
A novel phenylacetylene derivative containing the dicyanovinyl group (3) was successfully synthesized via Sonogashira coupling and a Knoevenagel reaction. Compound 3 could be used as a highly selective and sensitive turn-on fluorescent sensor for the detection of cyanide ions in aqueous solution. Upon the addition of cyanide ions, compound 3 changed from yellow to colorless which was readily observable by the naked eye. In addition, there was an increase of blue fluorescence emission under black light (365 nm) illumination. Using measurements of fluorescence intensity, the linear dynamic range for the quantitative analysis of cyanide concentration was determined to be 0–80 μM with a detection limit of 0.68 μM which is below the 1.9 μM limit recommended by the World Health Organization (WHO) for drinking water. 1H-NMR titration confirmed that the fluorescence turn-on signal is the result of a nucleophilic addition of the cyanide ion to the β-position of the dicyanovinyl carbon. The addition of the cyanide ion disrupts the π-conjugation between the fluorescent phenylacetylene unit and the strong electron withdrawing dicyanovinyl group, thus inhibiting the non-radiative intramolecular charge transfer (ICT) process. The application of compound 3 for the determination of cyanide in spiked samples of water and tapioca starch showed satisfactory results.
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