Dosimetric Chromogenic Probe for Selective Detection of Sulfide via Sol–Gel Methodology

Dinitrobenzenesulfonyl-protected naphthyl azo pyridine conjugate 1 has been designed and synthesized. Compound 1 acts as a nongelator in dimethyl sulfoxide (DMSO)–H₂O (1:1, v/v) while its hydroxy counterpart 2 can form a nice gel in the same solvent. In the presence of sulfide, compound 1 undergoes rapid sulfonate ester hydrolysis and results in the formation of azo-naphthol 2 that responds in instant gelation. Such deprotection was extremely selective to sulfide; other analytes did not show measurable response. The sensing mechanism has been established by various spectroscopic techniques. Compound 1 in solution (DMSO–H₂O) also shows a selective response toward sulfide over a series of other anions with a color change. Preparation of test kit with compound 1 allows detection of sulfide in solution and vapor states. Such kind of dosimetric sensing of chemical analytes by improvising the protection/deprotection of functional groups in gelator structure is rare in the literature, and to the best of our knowledge, this is the first example of a stimuli-responsive low-molecular-weight gelator which dosimetrically senses sulfide over other nucleophilic substrates.