Synthesis And Properties Of Pillar[5]arene Schiff Bases

Pillararene is one kind of aromatic cyclic oligomers,which consists of hydroquinone units linked by methylene bridges in the para position.Because it has similar appearance and shape to the column,it is named as "pillararene".In recent years,pillararene has been widely used in drug controlled release systems,artificial transmembrane channels,metal organic frameworks,sensing and detection,functional materials and so on.Due to its characteristics of structural stability,easy function,and good host-guest performance,the synthesis of functionalized pillararenes and applications in supramolecular fields have attracted more and more attention.In this paper,we have successfully synthesized a series of promising pillar[5]arene Schiff base derivatives,and studied their recognition properties to transition metal cations.The main results are as follows:1.Through carefully retrieving the known literature,we selected the suitable synthetic routes of pillar[5]arene derivatives,screened the process conditions,amplified the reaction and obtained the opitimized process conditions.2.We have synthesized twelve pillar[5]arene aldehyde derivatives by alkylation reaction of pillar[5]arenes with p-hydroxybenzaldehyde or vanillin.Subsequently,twenty-four pillar[5]arene Schiff bases were synthesized by condensation of pillar[5]arene aldehyde derivatives with salicylhydrazide or pyridylhydrazide.Then,the recognition properties of the obtained pillar[5]arene Schiff bases to the transition metal cations were investigated by UV spectroscopy.All the pillar[5]arene Schiff bases were characterized with NMR,IR,ESI-MS.Five single crystals were obtained and their crystal structures were detected by X-ray single crystal diffraction.3.The six functionalized pillar[5]arene containing free alkylamino groups were successfully prepared by using Gabriel amination reaction procedure.Then,twenty-four pillar[5]arene Schiff bases were synthesized by condensation of pillar[5]arene amine derivatives with salicylaldehyde,5-chlorosalicylicaldehyde,5-bromosalicylaldehyde,3,5-di(tertbutyl)salicylaldehyde.The recognition ability of the Schiff base and metal cations was studied by UV and fluorescence spectroscopy.All the compounds were characterized with NMR,IR,ESI-MS.Single crystals of eight compounds were obtained and their crystal structures were determined by X-ray single crystal diffraction.4.By using pillar[5]arene aromatic aldehyde derivatives as starting material,seventeen dipillar[5]arene derivatives and six pillar[5]arene trimers were obtained by several condensation reaction with corresponding pillar[5]arene acylhydrazines,pyridine-2,6-dicarbohydrazide,ethane-1,2-di(thiosemicarbazide),hexane-1,6-di(thiosemicarbazide).All the compounds were characterized with NMR,IR,ESI-MS.