Construction And Recognition/stimuli Response Properties Of Pillar[5]Arene-Based Fluorescent Supramolecular Systems

Supramolecular chemistry is a raising interdisciplinary discipline that researches the weak interaction between molecules and ions or molecules and molecules.The study of these weak interactions is favored increasingly by the scientists.As important representative molecules of supramolecular chemistry,macrocyclic compounds serve as a crucial role in pushing forward the study of supramolecular chemistry effectively.As a brand new class of macrocyclic compound,in addition to crown ethers,calixarenes,cyclodextrins,and cucurbiturils,pillararenes,have been actively studied since firstly synthesized and named by Ogoshi in 2008.Because of their symmetrical and rigid architecture,electron-rich cavities and easy functionalization,pillararenes have displayed excellent host–guest recognition properties with diverse guest molecules,attracting a lot of attention of many researchers.This paper focuses on the research of the construction methods and response properties of the fluorescent supramolecular systems based on pillararenes.This paper is elaborated from three parts:In the first part,we summarize the construction methods and response properties of the fluorescent supramolecular systems based on pillararenes.We first summarize pillar[n]arene-basedfluorescentsupramolecularsystemswithrecognition performance.Next,we highlight pillar[n]arene-based fluorescent supramolecular systems with stimulating response properties.Finally,we also introduce pillar[n]arene-based fluorescent supramolecular systems with both recognition and stimuli response properties.In the second part,we have synthesized a brand new fluorescent sensor（AHP5）,which comprises a thioacetohydrazone-bridged bispillar[5]arene.Sensor AHP5 could fluorescently sense CN^–anions with high selectivity and sensitivity(5.14×10^-88 mol L^-1).Simultaneously,despite being under identical conditions,other competitive anions were still unfavorable for the switch-on fluorescence.The recognition mechanism was studied by ¹H NMR,Job’s plot measurements,and mass spectrometry.AHP5 could recognize CN^–owing to the deprotonation procedure and concomitantly the breaking of intermolecular hydrogen bonds.Moreover,AHP5 could also high sensitively fluorescently detect CN^–by naked eye with a detection limit of 5×10^-4mol/L.Meanwhile,the thin film based on sensor AHP5 was maded,which could serve as a test kit for probing CN^–conveniently.Finally,AHP5 could detect cyanide in water samples.More importantly,this is the first example of a bispillararene-based sensor being synthesized for fluorescent recognition of cyanide anions in DMSO/H₂O（9:1,v/v）solution,which expands the application of bispillararenes in the detection and separation of toxic ions/molecules.Inthethirdpart,wehavedesignedandsynthesizedanovel metallosupramolecularpolypseudorotaxaneviaapillar[5]arene-based pseudo[3]rotaxane and zinc ion coordination.At a high concentration,this metallosupramolecular polypseudorotaxane could self-assemble and whereafter form a metallosupramolecular polypseudorotaxane gel（HP5₂·Zn·G）.In particular,by utilizing the dynamic nature of host–guest interactions,metal–ligand bonds,as well as hydrogen bonding interactions,this polypseudorotaxane gel HP5₂·Zn·G could pose multiple stimuli-responsive gel–sol phase transitions under different external stimuli,such as formaldehyde,competitive guests,temperature,and so forth.In addition,polypseudorotaxane gel HP5₂·Zn·G could detect Fe³⁺and Cu²⁺by fluorescence effectively.More importantly,polypseudorotaxane gel HP5₂·Zn·G could be work as an ultrasensitive fluorescent sensor for sensing Fe³⁺（8.93×10^-1010 mol/L）.At the same time,the detection limit was 4.57×10^-8mol/L for Cu²⁺,also showing superior sensitivity of HP5₂·Zn·G to Cu²⁺.Furthermore,thin films based on this polypseudorotaxane gel HP5₂·Zn·G were maded to serve as test kits for detecting Fe³⁺and Cu²⁺conveniently.It should be pointed out that a pillararene-based supramolecular polypseudorotaxane was applied for highly sensitive fluorescence recognition of metal ions for the first time,which expands the application of pillar[n]arene-based polypyrocyclohexanes in ion recognition.