Competitive intra- and inter-molecular proton transfer in hydroxynaphthyl benzothiazole: selective ratiometric sensing of acetate

The receptor, naphthalene based benzothiazole (NHBT) shows acetate selectivity in its absorbance and emission behavior among the various interfering anions. Substantially red shifted absorption band and fluorescence emission of NHBT in pure acetonitrile media were developed which drastically got enhanced upon addition of tetrabutylammonium acetate. Excited-state intermolecular proton transfer in the sensor-anion hydrogen-bonding complex was suggested to be the signaling mechanism. NHBT, a good hydrogen-bonding donor, the ESIPT process is inhibited by the formation of a strong acetate-NHBT intermolecular hydrogen bond complex, and the inhibition mechanism consequently results in ratiometric response in absorption and emission spectroscopy, respectively.