Benzothiazole possessing reversible and reusable selective chemosensor for fluoride detection based on inhibition of excited state intramolecular proton transfer

• Selective F− sensing by Benzothiazole aryl amide possessing p-OCH3 group.
• F− addition causes conspicuous color change from colorless to yellowish green.
• Inhibition of ESIPT responsible for red shift of absorption and fluorescence bands.
• Tuning of optical responses alternatively by adding F− and HSO4−.

A series of three benzothiazole derivatives BTBAs based on aryl amide groups have been developed, whose photophysical properties were remarkably changed by the presence of –OCH3 and –NO2 groups at para-position of aryl amides. Among these chemosensors, BTBA-OCH3 showed fluoride selectivity in its absorbance and emission behavior among the various interfering anions, along with conspicuous color change from colorless to yellowish green color. Substantially red shifted absorption as well as fluorescence band of BTBA-OCH3 in DMSO, was observed upon addition of F− ions. Inhibition of Excited State Intramolecular Proton Transfer (ESIPT) in sensor-anion deprotonated complex was suggested to be the signaling mechanism. 1H NMR titrations of the sensor with F− ions also supported deprotonation process. In particular, the spectral responses of this chemosensor could be tuned from side to side alternatively by adding F− and HSO4− anions in DMSO solvent.

Among various benzothiazole derivatives (BTBAs) based on aryl amide groups, BTBA-OCH3 selectively recognized F− ion in both ground and excited state due to F− induced deprotonation of amidic NH. This was also responsible for disappearance of enol form (peak at 430 nm) and simultaneous appearance of its keto form (new red shifted peak at 502 nm.Figure optionsDownload as PowerPoint slide