Synthesis Of Conjugated Pillar[5]arene And The Selective Host-guest Complexation Towards Nitrile Guests

Supramolecular chemistry is an important part of chemistry.The studies on the synthesis of new macrocyclic hosts and their host-guest chemistry are the core of supramolecular chemistry.pillar[5]arene was first reported in 2008 and soon developed as a new generation of macrocyclic host after the four generations of traditional macrocyclic hosts(crown ether,cyclodextrin,calixarene and cucurbituril),pillar[n]arenes are made of hydroquinones connected by methylene bridges at the para-position and its name of “pillararene” came after its pillar shape.Owing to their unique characteristecs,such as rich electronic structure,highly symmetry and rigidity,pillararenes show excellent host-guest properties and have been applied in the field of molecular machine,the controlled release of drugs,biocyte staining,chemical sensor,et al.Moreover,the ease of functionalizing pillar[n]arenes leads to a variety of new host derivatives and host-guest supramolecular systems with excellent self-assembly properties.Research works of this dissertation mainly include the synthesis of conjugated difunctionalized pillar[5]arenes with the substitution at both ends of one hydroquinone unit and its selective molecular recognition towards guests such as nitriles.The main contents are listed as follows:(1)A novel main-chain pillar[5]arene-based conjugated polymer(P1)have been prepared by the copolymerization of a difunctionalized pillar[5]arene and a diketopyrrolopyrrole-based monomer(DPP).Because of the DPP unit in its main chain,P1 showed good photophysical properties such as the strong emission centered at 587 nm.P1 can form a linear main-chain polypseudorotaxane through a selective complexation with adiponitrile other than with 1,4-dihalobutane and 1,4-bis(imidazol-1-yl)butane.Based on the specific binding characteristic,P1 was successfully used for the adsorption of adiponitrile in water.This may assist in devising novel supramolecular molecules to detect,adsorb and separate organic molecules in water.(2)To design a fluorescent probe,a novel main-chain pillar[5]arene-based conjugated organic molecule(H1)have been prepared by the Suzuki reaction of a difunctionalized pillar[5]arene and 2,3-di(pyridin-2-yl)quinoxaline groups.By using fluorometry and NMR,we systematically studied the host-guest propertied of H1 towards 16 kind of organic guests.When adding different kind of electron-deficient guests,the fluorescence quantum yield of H1 was enhanced in defferent degree.H1 portrayed good selectivity towards succinonitrile,and the association affinity to succinonitrile was at least 10 times higher than to other guests.This phenomenon is first found in pillararenes research area.The methanism of fluorescence enhancement by complexation of electron-deficient guests may be because the inclusion of guests decreased the mobility of the units.(3)The main-chain conjugated pillar[5]arene H1 could selectively detect succinonitrile as a fluorescence increasing probe.2,3-di(pyridin-2-yl)quinoxaline groups could be used as a silver recognition groups in colorimetric and fluorescence “turn off” way.Two opposite fluorescence change trends made H1 a good dual-functional fluorescent probe.Upon complexing G1,the fluorescence quantum yield of H1 increased and H1@G1 had lower limit of detection for guests than H1.At the same time,the selectivity of H1@G1 towards silver ions was not changed even though H1 complex electron-deficient guests.This work not only provide a new way to design and synthesize multi-functional probe but also afford a new method to lower the limit of detection of fluorescence probe.(4)To explore the impact of conjugated structure on the host-guest property of pillar[5]arene,we designed and synthesized some pillar[5]arene host molecules H3-H6 and studied their host-guest properties by NMR and fluorometry.We found that when conjugated benzene ring or thiophene to one benzene of pillar[5]arene,H3 and H4 showed weak binding affinity towards 1,4-dihalobutane and 1,4-di(1H-imidazol-1-yl)butane.H4 had larger association constant than H3 and H4,because benzene ring was conjugated to one benzene of pillar[5]arene by acetylene bond which leads to benzene ring had lower effect on the cavity of pillar[5]arene.H6 has largest association constant to 1,4-dihalobutane and 1,4-di(1Himidazol-1-yl)butane,because benzene was connected by ether bond and benzene had least effect on the cavity of pillar[5]arene.Through these results,it was found that the different location of conjuaged structure changed the host-guest properties of pillar[5]arene.This work provides a new way to change the host-guest property of pillararene.