Experimental and theoretical anion binding studies on coumarin linked thiourea and urea molecules

A series of coumarin linked thiourea and urea molecules 1–5 have been designed and synthesized. Thiourea-based monotopic receptors 1–4 showed selective sensing of F− and C6H5COO− by exhibiting significant change in emission as well as change in color. The ditopic receptor 5, on the other hand, fluorometrically distinguished isomeric aromatic dicarboxylates in polar solvent DMSO. Theoretical calculations have been carried out on systems 1–4 and their complexes with C6H5COO− and F− anions in the presence of CH3CN solvent. Calculations have been carried out to determine the geometry and bonding of the complexes in the ground electronic state as well as on the excited electronic states relevant to the absorption spectra and emission spectra in an effort to obtain information on the spectral changes accompanying complexation of the receptors 1–4 with the two anions.