Azacrown-CH2-bipyridine receptors in silica xerogel.Optical and coordination properties

Abstract

Samples of silica xerogel doped with encapsulated series of three receptors of the type (aza-3n-crown-n)-CH₂-(2,2′-bipyridine), where n=4, 5 and 6, were prepared by the sol–gel process. Fluorescence excitation spectra of the encapsulated receptors differ from the absorption spectra. Emission of the samples can be quenched specifically owing to the coordination reaction with transition metal ions. Emission decays can be described by a double exponential, the lifetime values being short at room temperature. EPR spectra of Cu^II ions complexed on the surface of the receptor doped xerogel have fairly well resolved hyperfine structure and show an elongated rhombic octahedral environment for the receptors with 2,2′-bipyridine groups.