Unique Fluorogenic Ratiometric Fluorescent Chemodosimeter for Rapid Sensing of CN− in Water

A new benzimidazole‐spiropyran conjugate chemosensor molecule (BISP) has been synthesized and characterized by 1H NMR spectroscopy, mass spectrometry (ESI‐MS), and elemental analysis. The two isomeric forms (BISP↔BIMC) were shown to be highly selective and sensitive to CN− among the ten anions studied in aqueous HEPES buffer, as shown by fluorescence and absorption spectroscopy and even by visual color changes, with a detection limit of 1.7 μM for BIMC. The reaction of CN− with BIMC was monitored by 1H NMR spectroscopy, high‐resolution mass spectrometry (HRMS), UV/Vis measurements, and fluorescence spectroscopy in HEPES buffer of pH 7.4. TDDFT calculations were performed in order to correlate the electronic properties of the chemosensor with its cyanide complex. Further, titration against thiophilic metal ions like Au3+, Cu2+, Ag+, and Hg2+ with [BIMC‐CN] in situ showed that it acts as a secondary recognition ensemble toward Au3+ and Cu2+ by switch‐on fluorescence. In addition, a reversible logic‐gate property of BIMC has been demonstrated through a feedback loop in the presence of CN− and Au3+ ions, respectively. Furthermore, the use of BIMC to detect CN− in live cells by fluorescence imaging has also been demonstrated. Notably, test strips based on BIMC were fabricated, which could serve as convenient and efficient CN− test kits. Sense and Sensitivity: A new benzimidazole‐spiropyran conjugate chemosensor molecule (BISP) was synthesized and characterized. The two isomeric forms (BISP↔BIMC) were shown to be highly selective and sensitive to CN− in aqueous HEPES buffer, with a detection limit of 1.7 μM for BIMC.