Synthesis,Structure,and Property Of Fluorescent Sensors Based On Aza-and Oxacalix[4]arenes

Calixarenes,known as the third-generation of macrocyclic host molecules in the field of supramolecular chemistry,have attracted wide attention in molecular recognition and sensing,self-assembly,drug transmission,etc.Heterocalixarenes,by replacing the bridging methylene groups with heteroatoms,have become a new research hot topic because the introduction of heteroatoms endows them with novel structures,flexible and tunable conformations.Since the beginning of this century,azacalix[4]arenes and oxacalix[4]arenes have quickly become excellent platforms for further functionalization due to the breakthrough in synthesis.In this thesis,we developed cation and anion fluorescent sensors based on these two platforms.（1）We developed a one-pot method for the synthesis of azacalix[4]arenes via four folds of aromatic nucleophilic substitution reactions.After Pd/C catalyzed hydrogen reduction of nitro groups into amino groups,the reactions between various aromatic aldehydes and tetra（NH₂）azacalix[4]arene at the bridging NH and NH₂ positions provided imidazobenzimidazole,which was confirmed by X-ray single crystal diffraction analysis.The pyrenyl attached imidazobenzimidazole fused azacalix[4]arene showed naked-eye detected color change and fluorescence color and intensity changes,which could be used as a fluorescent sensor for the specific recognition of zinc ions.UV-visible and fluorescence spectroscopic experiments further revealed a 1:1 binding mode for the sensor zinc ion,with a binding constant of 1.1×10⁵ M^-1and a limit of detection of 2.3×10^-6 M.The specific recognition process also exhibited anti-interference and complete reversibility.（2）Through the formation of imide bonds and subsequent reduction reactions,we synthesized anthracenyl and pyrenyl fluorophores modified oxacalix[4]arenes.The fluorescence of the two host molecules was weak due to the PET effect.Upon addition of trifluoroacetic acid to protonate NH,the fluorescence of the host molecules recovered.After screening,the pyrenyl modified oxacalix[4]arene showed specific recognition ability toward NO₃^-,which could be confirmed by naked eye recognizable color change,UV-vis spectroscopy,and fluorescence emission spectroscopy.Anthracenyl modified oxacalix[4]arene showed no selective recognition toward various anions.