Construction And Properties Of FRET-based Fluorescent Supramolecular Assembly Systems

As one of the emphases and core contents of supramolecular chemistry,self-assembly has been known as an important method to create new substances and produce new functions at the molecular level.Through coordination-driven self-assembly,there have successfully constructed a large number of two-dimensional(2-D)or three-dimensional(3-D)discrete supramolecular metal-organic self-assembly systems with regular geometry.At present,coordination-driven self-assembly,which is based on metal-ligand coordination interactions,has proven to be an efficient strategy for the construction of discrete supramolecular metal-organic self-assembly systems with precise and controllable structures of the shape,size and cavity,which are widely used in catalysis,photoelectric materials,gas storage,biological applications and other fields.So far,there are many reports about the construction,properties and functions of discrete supramolecular metal-organic self-assembly systems.However,less research has been reported on the process and mechanism of self-assembly,which is of great scientific significance for understanding the essence of assembly,revealing the assembly rules and guiding the design of functional supramolecular self-assembly systems.Combing with our long-term research background around the coordination-driven self-assembly,the thesis will construct a series of fluorescent functionalized supramolecular self-assembly systems based on fluorescence resonance energy transfer(FRET)through the strategy of coordination-driven self-assembly.On the one hand,FRET technology has been used to study the assembly process and mechanism of multi-level assembly system;on the other hand,based on the understanding of the mechanism of self-asssembly,a series of FRET supramolecular metallacycles and metallacages will be designed rationally,and explore their functions and applications in the fields of photocatalysis and light-harvesting.The thesis can be divided into five parts,the details are shown below:In chapter one,there are overviews of the construction strategy of discrete supramolecular metal-organic self-assembly based on coordination-driven self-assembly.In addition,a detailed introduction to discrete fluorescent supramolecular metal-organic self-assembly,including the construction strategy and applications,is demonstrated.In chapter two,a two-step FRET system bearing specific numbers of anthracene,coumarin,and BODIPY moieties at precise distances and locations through an efficient and controllable orthogonal self-assembly approach based on metal-ligand coordination and host-guest interactions,was successfully fabricated,and then successfully studied the multi-component and multi-level controllable assembly process through the multi-FRET,which provided a good foundation for the study of the assembly process and mechanism of the multi-level assembly system.By introducing anthracene and coumarin fluorophores into the assembly ligand,the FRET-based metallacycle was successfully constructed by coordination-driven self-assembly,which was used to monitor the self-assembly progress and the dynamic ligand exchange.Furthermore,pillar[5]arene modified with BODIPY was introduced as receptors to construct the second-step energy transfer system through host-guest interaction.The research shows that the two-step FRET system can be successfully fabricated via either stepwise self-assembly or one-pot orthogonal self-assembly.Meanwhile,compared with the one-step FRET system,the construction of multi-FRET system can improve the singlet generation efficiency and photocatalytic activity of the BODIPY photosensitizer in the system.In chapter three,discrete and highly symmetrical hexagonal metallacycles with FRET-based and heavy atom effect,was constructed for efficient photosensitization efficiency and photocatalytic activity through coordination-driven self-assembly of120° coumarin-containing dipyridyl donor and 120° diiodo-BODIPY-containing diplatinum(II)accepter.In comparison,FRET-based metallacycles displayed higher photosensitization efficiency and photocatalytic activity.More importantly,metallacycles with iodination showed higher photosensitive efficiency and photocatalytic activity than metallacycles without iodination.Therefore,the photosensitive efficiency and photocatalytic activity of the supramolecular fluorescent metallacycles were simultaneously improved by FRET strategy and heavy atom efficiency.In addition,supramolecular fluorescent metallacycles,as a high-efficiency photocatalyst for the catalytic oxidation of sulfide,have good substrate universality and selectivity.In chapter four,a supramolecular artificial light-harvesting system with continuous energy transfer process with the coordination-driven self-assembly,host-guest interaction and hydrophobic interaction as the core driving forces,are fabricated.Firstly,a discrete and highly symmetrical hexagonal metallacycle was constructed by 120° TPE-containing dipyridyl donor and 120° diplatinum(II)accepter through coordination-driven self-assembly.Then,stable host-guest complexes were constructed by the host-guest interactions between the nitrile and pillar[5]arene modified with BODIPY or DSA,which exhibit high fluorescence emission under solvent induction to form nanoparticles with AIE enhancement(AIEE)and FRET.In addition,the hydrophobic dye Nile red was introduced to further construct supramolecular artificial light-harvesting system with high antenna effect and high energy transfer efficiency.In chapter five,a supramolecular artificial light-harvesting system with continuous energy transfer process and photocatalytic ability was prepared by self-assembly of metallacage and amphiphilic polymer and hydrophobic interaction in aqueous phase.The construction of FRET-based tetragonal prismatic metallacage between TPE face and BODIPY pillar through coordination-driven self-assembly.Then,an amphiphilic polymer,m PEG-DSPE,was used to incorporate metallacage forming the nanoparticles.In addition,the hydrophobic dye Nile red was introduced to further construct supramolecular artificial light-harvesting system with continuous energy transfer process in an aqueous phase with excellent light-harvesting ability.Further,the supramolecular artificial light-harvesting system can be utilized as an nanoreactor for photocatalyzed dehalogenation of α-bromo-4’-methoxyacetophenone in aqueous medium,which improves the catalytic effect and shows a broad application prospect in the field of biomimetic catalysis.In this thesis,a series of fluorescent supramolecular metal-organic self-assembly systems with FRET properties were constructed through coordination-driven self-assembly strategy by rationalizing the design of fluorescent ligands.The assembly process and mechanism of multi-component and multi-level complex supramolecular assemblies were studied through the multi-FRET.In addition,some fluorescent functionalized supramolecular metal-organic assemblies were further developed and then studied the properties of photocatalyst and photocatalysis.