Selective Sensing of Anions with Calix[4]pyrroles Strapped with Chromogenic Dipyrrolylquinoxalines

Abstract

New calix[4]pyrroles bearing dipyrrolylquinoxaline as strapping elements have been synthesized and characterized by spectroscopic means. The binding behavior of these receptors at 25 degrees C was investigated first by proton NMR spectroscopy in CD(3)CN/DMSO-d(6) (9:1 v/v), as well as by UV-vis spectroscopy and isothermal titration calorimetry (ITC) in CH(3)CN/DMSO (97:3 v/v). The receptors displayed a selective colorimetric response when exposed to the fluoride, dihydrogen phosphate, and acetate anions (studied in the form of the corresponding tetrabutylammonium salts) and an enhanced affinity as compared to a comparable calix[4]pyrrole system lacking the dipyrrolylquinoxaline-containing strap.