Coumarin-Strapped Calix[4]pyrrole: A Fluorogenic Anion Receptor Modulated by Cation and Anion Binding

摘要

We have succeeded in synthesizing a strapped calix[4]pyrrole-coumarin conjugate 1. Association constants (K_a) corresponding to the interaction 1 with Cl~-, Br~-, and AcO~- anions were determined using fluorescence titrations carried out in the presence of Na~+ (or H_2O) and gave values concordant with those determined using ITC. The fluorescence emission properties of 1 were found to depend on the environment and could be specifically controlled via the addition of Na~+ (or H_2O) and anions. In acetonitrile, fluorescence quenching by anions is only observed in the presence of H_2O or cations, such as Na~+. These and other observations are consistent with the presumed PET process being controlled by both cation and anion recognition. We believe that our approach, involving the strapping of calix[4]pyrroles with fluorophores, will emerge as a powerful new approach to the design of "smart" molecular devices whose "logic" function can be controlled by ion or, in due course, neutral substrate recognition.