A ratiometric fluorescence chemosensor based on a coumarin–pyrazolone hybrid: the synthesis and an investigation of the photophysical, tautomeric and anion binding properties by spectroscopic techniques and DFT calculations

Abstract

A fluorescent chemosensor (C-2) having a coumarin ring as a signalling unit and a pyrazolone ring as an H-donor receptor was synthesized for the purpose of recognition of anions in DMSO. The most stable tautomeric form of C-2 was determined using spectroscopic techniques and DFT calculations. The absorption and emission behaviours of C-2 were investigated in solvents of different polarities to confirm the expected tautomeric forms. The absorption and emission bands were blue shifted with increasing solvent polarity because of negative solvatochromism. The selectivity of C-2 for F−, Cl−, Br−, I− and AcO− anions was determined in DMSO and it was found to be suitable for the detection of F− in the presence of Cl−, Br−, I− and AcO− as competing anions at the stoichiometric ratio of 1:1.