Iminocoumarin based fluorophores: Indispensable scaffolds for rapid, selective and sensitive detection of thiophenol

• Iminocoumarin based probes for rapid and selective detection of thiophenol are reported.
• A correlation between response times with predicted pKaH values of respective fluorophores was established.
• Benzothiazole probe showed 260-fold off-on fluorescent enhancement upon thiophenol sensing.
• Detection limit of 6.9 × 10−9 M was calculated for Benzothiazole probe.

Off-on fluorescence probes for the detection of thiophenol were designed based on the reaction mechanism to ensure rapid sensing process. 2,4-Dinitrophenylsulfonyl based probes with iminocoumarin fluorophores were validated by theoretical calculations for their off-fluorescence states. Reaction of these probes with thiophenol released strong fluorescent iminocoumarin species with good response times. These results, upon comparing with reported probes, confirmed that higher pKaH values of the imino nitrogen of iminocoumarins are important for rapid sensing process. Reactivity of these probes was limited to only thiophenol and no reaction was observed with aliphatic thiols. The benzothiazole substituted probe displayed up to 260-fold fluorescence enhancement upon reaction with thiophenol. Sensing of the analyte by the probe was characterized by change in color from red to yellow and with appearance of the green fluorescence. A detection limit up to 6.9 × 10−9 M was also determined for this probe.

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