Theoretical Prediction Of Structures And Properties For Heteroatom-bridged Pillar[n]Arenes

Pillar[n]arenes are one of the supramolecular macrocyclic compounds in wide application prospects with properties of rigid structures and being functionalized easily.In order to enrich the types of pillar[n]arenes,heteroatom-bridged pillar[n]arenes PnX(n=4,5,6 X=B,N,O,Si,S,P,Se)—a class of new pillar[n]arenes is put forward in this paper by replacing the bridge methylene group with heteroatoms differently from traditional derivatization way.The structure and properties of heteroatom-bridged pillar[n]arenes are predicted by Density Fuctional Theory(DFT),and the cause of special properties of heteroatom-bridged pillar[n]arenes are investigated from the microcosmic aspects.The purpose of this study is to enrich the derivatives of pillararenes and provide theoretical basis for the synthesis of PnX in experiment.The work of this paper is divided into the following three aspects:1)The host-guest interaction between structural rigid host—per-hydroxylated pillar[4]arenes(P4A)and guests——monovalent cation,anions(NH4+,HCO3-,NO3-,H2PO4-,HSO4-,Br-,Cl-)and neutral molecules(Arginine and Fosmidomycin)are investigated by DFT method to clarify the idea of designing and analysing pillararenes system using theoretical calculation.The results show that guests@P4A are stable through hydrogen bonds interacted by anions,cation,neutral molecules and P4A as well as X-H… interaction(X=C,N,O,etc.)between X-H groups of guests and the electron-rich benzene ring of pillar[4]arene.Increasing the numbers of hydrogen bonds between P4A and guests,shortening the distance of the hydrogen bonds and selecting the guests with strong conjugation ability are conducive to charge transfer between the host-guest complexes and dispersing the overall charge,which can enhance the host-guest inclusion ability.Besides,the volume of molecular and steric effects between guests and P4A are ought to be balanced.The weak interaction and steric effects in this system are visualized by combining the Reduced Density Gradient(RDG)function and colored filling isosurface.2)A new type of heteroatom-bridged pillar[n]arenes PnX(n=4,5,6;X=B,N,O)is proposed theoretically for the first time.The molecular structures of PnX are obtained at the calculation level of ωB97XD/6-311G(d,p).The electronic structure,spectral properties,solvent effects and host-guest properties between PnXs and paraquat are systematically researched.Results show that the electron-deficient Boron atom tend to bond in sp2 leading to the deflection of benzene ring unit and molecular structures become more flexible and electron conjugation is increased,thus two characteristic peaks at 250-280 nm and 350-380 nm are observed.Meanwhile,the electron density on benzene unit of PnB decreases causing the weakened ability of complexation with paraquat.Nitrogen and Oxygen atoms with lone pair electrons tend to bond in sp3 as Carbon atoms do,so the molecules structure of PnN and PnO maintain the original rigidity.The complexation ability with paraquat strengthens with the electron density on the benzene ring rises.The solubility of PnX is higher in polar solvents,and increases with degree of polymerization n.3)The second kind of heteroatom-bridged pillar[n]arenes PnX(n=4,5,6;X=Si,P,S,Se)are designed to further explore the structure,electronic properties,spectral properties,solvent effects and host-guest properties of PnX series.The results show that molecular flexibility of the PnX increases due to larger atomic radius of these bridged heteroatoms.Thus,the electron conjugation effect of PnX are strengthened,the UV absorption peak redshifts to 290 nm.The other peak occurs at 210 nm-230 nm because of the more flexible structure of PnSi and PnP.The structure matching ability with paraquat of PnX decreases due to the increase of the molecular cavity and the reduction of electron density on benzene.Flexible molecular structure may cause the internal interaction of hydroxyl groups on the benzene ring of PnX which decreases solubility in various solvents.To sum up,the introduction of heteroatoms Boron,Silicon,Sulfur,Phosphorus,Selenium will increase the structural flexibility of PnX,enhance the electron conjugation ability of PnX,redshift the UV absorption spectrum,even peak near the low wavelength,and reduce the solubility of PnX.While the introduction of Oxygen and Nitrogen atoms is quite the opposite;The increase and decrease of the electron cloud on benzene unit caused by the bridged heteroatoms will respectively strengthen and weaken the interaction between PnX and paraquat.