A new disulfide Schiff base as a 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 the S-S bond and nucleophilic attack of the cyanide ion on the imine group of the disulfide chemosensor with a 1 : 2 binding stoichiometry, as confirmed by H-1 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 x 10(-7) M. The L chemosensor is used successfully for the detection of cyanide in electroplating wastewater and the 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 the [L-CN-] system is quenched by Fe3+ ions and can be used as a sensitive and selective ON-OFF fluorescent sensor for the detection of Fe3+. The fluorogenic sensing can be applied for the fabrication of an INHIBIT type molecular logic gate.