A new disulfide Schiff base as versatile “OFF-ON-OFF” fluorescent-colorimetric chemosensor for sequential detection of CN− and Fe3+ ions: Combined experimental and theoretical studies

A new naphthaldehyde based disulfide fluorogenic and colorimetric chemosensor, N, N´ disulfandiylbis(2,1-phenylene))bis(1-(naphthalene-1-yl)methaneimine) (L), has been synthesized, and characterized by CHN analyses, X-ray crystallography and different spectroscopic methods. The detection of cyanide is accompanied by the cleavage of S-S bond and nucleophilic attack of cyanide ion on the imine group of the disulfide chemosensor with a 1:2 binding stoichiometry, as confirmed by 1H NMR studies. The specific reaction results in a significant fluorescence enhancement and a color change from pale yellow to orange. The LOD for cyanide detection is 2.5×10-7 M. The L chemosensor is used successfully for detection of cyanide in the electroplating wastewater and fabrication of colorimetric test strips. The colorimetric and fluorogenic sensing mechanism of L toward CN¯ is also investigated by DFT calculations and ESI-MS experiments. The emission of [L-CN¯] system is quenched by Fe3+ ions and can be used as a sensitive and selective “ON-OFF” fluorescence sensor for detection of Fe3+. The fluorogenic sensing can be applied for the fabrication of an INHIBIT type molecular logic gate.