Preorganized Platinum(?)-Based Supramolecular Systems

Supramolecular chemistry is a subject that uses non-covalent bonds between molecules to assemble them into complex,ordered and functional aggregates.Compared with covalent bonds,the energy of non-covalent bonds is relatively lower.This feature gives the dynamic reversibility of weak interactions and the advantage of responsiveness to external environmental stimuli.How to use weak non-covalent bonds to achieve complex and powerful functional assembly is the main direction and research task of the development of supramolecular chemistry.Supramolecular materials constructed based on weak non-covalent bonds have been widely used in drug delivery,photocatalysis,surfactants and other fields.However,the existing weak non covalent driving forces are mainly limited to hydrogen bonds,donors and acceptors,?-?,metal coordination,etc.Therefore,how to develop new types of weak non-covalent bonds and the cooperative interaction of multiple weak non-covalent bonds?The construction of functional supramolecular assemblies is still a research hotspot in supramolecular chemistry.The d8 electron configuration platinum(?)complex possesses a plane square structure and coordination unsaturation,which makes it an ideal supramolecular building block.This type of compound is very easy to produce platinum(?)platinum(?)metal metal interaction during assembly,thus giving the attractive photophysical and photochemical properties of the assembly,especially the platinum complex with a ?plane.In the past ten years,our research group has conducted systematic research on the host-guest supramolecular system of N^N^N and C^N^C platinum(?)complexes,and constructed a series of platinum(?)complex based on the tweezing-oriented strategy.The supramolecular tweezers can recognize multiple objects such as aromatic hydrocarbons,hydrogen bond donor molecules,metal organic complexes,etc.through donor acceptor,hydrogen bond and platinum(?)platinum(?)metal metal interaction.A variety of functional supramolecular tweezers have been constructed by our group.In order to expand the work of the tweezer-oriented system,during my Ph.D.period,I still used the organoplatinum(?)complex as a platform,through multiple platinum-platinum interactions,?-? stacking interactions,and metal coordination bonds to build the environmental responsiveness host-guest complexes and metal supramolecular polymers.Specifically,this paper is divided into the following four parts.In the first part of the research work,based on our groups previous research on supramolecular tweezers,the N^N^N molecular tweezers have a strong binding effect on fused ring aromatic hydrocarbons and neutral platinum(?)mononuclear complexes.From the perspective of the lack of electricity of the organoplatinum(?)complex,we designed and synthesized N^N^N-type self-complexing molecular tweezer by using the dual roles of the terpyridine structure(rigid linking element and guest molecule),and through 1H NMR,1H-1H ROESY?etc.verified the structure of the dimer,calculated the strength of self-complexation,and investigated the stability of the dimer in different solvents.At the same time,the reversible regulation of the dimer structure by cations was studied.In addition,the self-complexing molecular tweezers can be destroyed by adding the electron-rich guest molecule carbazole to form tweezers/carbazole complexes.The emission intensity of the molecular tweezers decreases,and a new emission peak appears at 622 nm,accompanied by the color change of the solution.In the second part of the research work,our group's early research on N^N^N-type organoplatinum(?)complexes are mostly ADA or DAD-type supramolecular tweezing system,and they were all studied in the organic phase.We want to increase the strength of the host-guest complex and introduce water during the assembly process.We designed and synthesized two hydrophilic and hydrophobic AA(positive charge)and DD(neutral)molecular tweezers.We want to enhance the binding ability of the two through the multiple platinum(?)-platinum(?)metal-metal interaction and ?-? stacking formed after assembled.First,the bonding strength of the two was studied,and it was found that the bonding strength was two orders of magnitude higher than the ADA or DAD type assembly.According to the research findings,an obvious MMLCT peak appeared after the assembly was formed,indicating that platinum platinum metal metal interactions were produced.UV-Vis Job-plot proves that the two are 1:1 complex,and it is verified by isothermal calorimetric titration.Then the assembly mechanism of the two in the mixed solvent system was studied,and it was discovered that it was a cooperativity mechanism in THF/H2O,and an isodesmic mechanism in THF/MCH.Furthermore,the size and morphology of the two assemblies were tested by TEM and DLS.The size in THF is about 1 nm,and the size in THF/H2O and THF/MCH is about 150 nm.It can be seen that the sizes are different from various solvents.In the third part of the research work,the distance between the two arms of the N^N^N or C^N^C molecular tweezers is about 7 A.We want to reduce the distance between the two arms of the molecular tweezers and at the same time decrease the cavity.Based on the above reasons,we replaced the rigid linking block in the N^N^N molecular tweezers with[2.2](1,4)cyclophane.The distance between the two benzene rings in the cyclophane is 3.09 A,which is smaller than the distance of ?-?stacking interactions.At the same time,a control molecular tweezer(terpyridine structure is replaced by long alkylated terpyridine)is designed.First of all,we studied the spectrum of molecular tweezers and found that the molecules themselves have no fluorescence.Temperature dependence experiments show that molecular tweezers have strong stability.Finally,the responsiveness of the molecular tweezers to cation ions was investigated,and it was found that silver ions make molecule have a strong fluorescence signal around 700 nm.The phenomenon did not appear in the control molecular tweezer.In the fourth part of the research work,based on the interesting photophysical properties of organoplatinum(?)complex.Metal coordination is used as a non-covalent link to construct rigid metal supramolecular polymers.The benzothiadiazole functionalized binuclear platinum(?)alkyne moiety endows excellent photophysical properties to the monomer.The process of supramolecular polymerization was studied by 1HNMR,UV-visible spectroscopy,isothermal titration and quantitative calorimetry,two-dimensional diffusion sequencing nuclear magnetic resonance,and viscosity experimental methods.In addition,the reversibility of assembly is achieved by adding a competitive ligand to the metal supramolecular polymer.The metal supramolecular polymer has fluorescent switching properties.