Synthesis,Characterization,and Luminescent Properties Of Platinum(Ⅱ) Complex-Containing Polymers

Metal-containing polymers are composed of polymeric chains,metal centers,and/or metal-related segments.The dynamic,noncovalent nature of the metal-ligand coordination endows metal-containing polymers with stimuli-responsive,adaptive,and self-healing properties.Meanwhile,the metal-containing polymers retain the catalytic activities,magnetic properties,and luminescent behaviors of the metal-ligand complexes,respectively.Moreover,metal-containing block copolymers can self-assemble in selective solvents to construct morphology-controllable nanodomains filled with metal-related segments or metal-ligand complexes.The note is that the metal-ligand complexes obtained with 2,2′:6′,2″-terpyridine or 2,6-bis（benzimidazol-2′-yl）pyridine（bzimpy）occupy sizes ranging from 1 to 3 nm.These metal-ligand complexes,for example,[Pt（bzimpy）Cl]⁺（1.2×1.0 nm²）,can be conceptually regarded as an individual building.In this context,the resulting[Pt（bzimpy）Cl]⁺-containing polymers can self-assemble in solution to generate micelle-like aggregates such as spherical micelles,wormlike micelles,vesicles,and nanosheets.Their phosphorescence emissions and quantum yields are intensified significantly as a result of increasing Pt（Ⅱ）···Pt（Ⅱ）and/orπ-πstacking interaction.Such research work is of fundamental importance for their potential applications in materials science and biological functions.However,the microphase separation between polymeric segments and metal–ligand complexes has been less addressed,which is critical to control their structures and functions.Based on this,the research of this doctoral dissertation includes three parts as follows:In our first work,we report on the synthesis of short-chain polystyrenes（PS）end-functionalized with[Pt（bzimpy）Cl]⁺complexes（PS_nPt-I and PS_nPt-Ⅱ,n=14,19,24,34,41,53,73）.The platinum（Ⅱ）-comprising polymers show significant luminescence enhancements in chloroform/methanol solvent mixtures with increasing the methanol composition.Controllably modulating the PS length and solvent quality leads to the sequential fabrication of nanofibers,nanoellipsoids,and nanospheres.Most significantly,the inside structures of these polymer particles are shown to be lamellar with sub-10 nm spacings,wherein the PS block are alternatively aligned with the platinum（Ⅱ）units.Such luminescence enhancements and hierarchical nanostructured particles originate from a subtle combination of directional Pt（Ⅱ）···Pt（Ⅱ）and/orπ-πstacking interactions between the platinum（Ⅱ）units and solvophobic effect between the PS blocks.This work suggests that by microphase separating polymer chains with nanosized metal-ligand complexes,metal-containing polymers can self-assemble to form sub-10 nm scale nanostructures showcasing desired properties and functions.In our second work,we report on the synthesis of a novel class of diblock polymer ligands,poly（ethylene oxide）-block-polystyrenes（PEO-b-PS）end-functionalized with bzimpy,and their coordination reactions with K₂Pt Cl₄ to create platinum（Ⅱ）-containing diblock copolymers（PEO45PSn Pt-I and PEO45PSn Pt-Ⅱ,n=115,150,189,208,280,410）.The planar[Pt（bzimpy）Cl]⁺end possesses a nanometric size（1.2×1.0 nm²）,and can be readily regarded as an individual block in the resulting copolymers.They demonstrate phosphorescence enhancements in both THF-water and 1,4-dioxane-n-hexane mixed solvents,arising from Pt（Ⅱ）···Pt（Ⅱ）and/orπ-πstacking interactions between the planar[Pt（bzimpy）Cl]⁺units.Correspondingly,the block copolymers demonstrate a solvent-tunable self-assembly behavior to controllably generate vesicles and worms with core-shell-corona architectures.In these nanostructures,the planar[Pt（bzimpy）Cl]⁺blocks are associated together to form cores driven by Pt（Ⅱ）···Pt（Ⅱ）and/orπ-πstacking interactions.The cores are completely isolated by PS shells,which are further encapsulated by PEO coronas.Such core-shell-corona nanostructures are more hierarchical than those previous core-corona micelles formed by[Pt（bzimpy）Cl]⁺end-functionalized homopolymers or PEO-b-PS.It should be highlighted here that diblock polymers are for the first time coupled with phosphorescence platinum（Ⅱ）complexes,representing a novel approach to create functional metal-containing polymer materials with hierarchical architectures.In our third work,two series of 4-arm polymers were obtained with platinum（Ⅱ）complexes tethered onto the ends of 4-arm starlike polyethylene glycol（PEG）via the combination of click reaction and coordination chemistry（4-PEG_nPt-I and 4-PEG_nPt-Ⅱ,n=45,114,228,456）.The resulting 4-arm metallopolymers exhibited luminescence enhancements upon increasing the water content in DMSO.The mechanism for such luminescence enhancements was attributed to the formation of Pt（Ⅱ）···Pt（Ⅱ）and/orπ-πstacking interactions.Furthermore,these 4-arm metallopolymers can self-assemble to form spherical micelles with a core of the platinum（Ⅱ）blocks and a corona of 4-arm PEG in the DMSO/water mixture solvent with the water volume content to be 60%.These platinum（Ⅱ）-containing block polymers show solvent-tunable phosphorescent emissions,self-assembled hierarchical nanostructures and microphase separation behavior between[Pt（bzimpy）Cl]⁺and polystyrene,which probably demonstrate potential applications in the fields of luminescence sensing,bioimaging,and/or controlled drug release.