Optical Chemosensory Studies of Novel Amphiphilic D-A-π-A Benzothiadiazoles for Cyanide Detection

Two positively charged amphiphilic benzothiadiazoles (2–3), functionalized with 2,3-dimethylbenzo[d]thiazol-3-ium and 2,3-dimethylnaphtho[2,1-d]thiazol-3-ium acceptor moieties, synthesized earlier in our research group, from 7-(4-methoxyphenyl)benzo[c][1,2,5]thiadiazole-4-carbaldehyde (1), were evaluated concerning their optical chemosensory capabilities towards different anions in DMSO and in a DMSO/water (75:25). Spectrophotometric and spectrofluorimetric titrations were performed demonstrating that both compounds were highly sensitive to cyanide in DMSO. Compound 2 showed fluorescence quenching at 657 nm with 5 equivalents of CN⁻, while compound 3 displayed a decrease in absorption at 480 nm and emission at 666 nm with 7 equivalents of CN⁻ in DMSO solution. Nevertheless, in DMSO/water mixture, the sensitivity decreased, requiring 50–70 equivalents of cyanide for fluorescence quenching.