Exploratory studies towards various anion recognition chemistry by two different sized cleft shaped organic ligands.

Indole and urea based two organic receptors have been synthesized by an easy synthetic process. These two receptors have strong sensitivity and selectivity for several bio-relevant anions. Receptor 1 and 2 were synthesized from indole-2-carboxylic acid and p-anisidine respectively, which are low cost starting materials. Receptor 1 can selectively sense anions like F(-), OAc(-) and H2PO4(-), while receptor 2 can only sense F(-) and H2PO4(-). Both receptors are silent toward anions like Cl(-), Br(-), I(-) and NO3(-). It is the difference in their shape and size which are responsible for different anion sensing. The nature of these host-guest type interactions was analyzed by convenient spectrophotometric techniques like UV-Vis, fluorescence, (1)H NMR, FT-IR studies and also confirmed by electrochemical techniques like cyclic voltammetry studies of the two ligand receptors with convenient anions. Between receptor 1 and 2, receptor 2 was crystallographically characterized also.