End-Functionalized Linear And Star Polymers: Photophysical Properties And Self-Assembled Nanostructures

Polymers have been widely used in materials science and life sciences,which are different from small molecules with properties such as high elastic deformation and viscoelasticity.The star-shaped polymers have different properties and functions coming from the linear polymers due to their unique topological structure.They also constitute a unique class of nanomaterials with unique rheological and thermodynamic properties,and these nanomaterials have also been applied to life sciences and nanotechnology.It has been a common means of designing and synthesizing novel polymer materials with novel structures and properties by modifying these linear or star-shaped polymers.Transition platinum（Ⅱ）complexes have d⁸ electronic conformation and a square-planar structure.Platinum（II）complexes can get close to each other so that the orbitals of the metal centers overlap with each other,forming new energy level orbitals.Therefore,metal-metal interactions lead to molecular stacking resulting in new excited states.Platinum（II）complexes exhibit strong triplet luminescence（long luminescence lifetime,high quantum yield,and adjustable excited state properties,etc.）in solution and solid states.Novel molecular structures with characteristic luminescent properties and self-assembled structures can be designed and synthesized by utilizing the luminescence and molecular packing properties of square-planar platinum（Ⅱ）complexes.Novel materials can be achieved from the doping and modification of polyoxometalates with other materials,or the combination of polyoxometalates with inorganic,organic molecules,and ions.The resulting hybrids not only have the specific properties of each component,but also some new functions,which can be applied to more fields.Novel polymers having the desired properties and functions can be obtained by introducing platinum（Ⅱ）and polyoxometalates into linear or star-shaped polymers.In addition,block copolymers can self-assemble into nanostructures such as vesicles and unimolecular micelles in selective solvents.The potential of these block copolymers with specific nanostructures can be continuously explored,especially in the fields of drug delivery,catalysis,and material science.1.We have prepared luminescence planar-coil SBCs by electrostatic combination of a cationic platinum（Ⅱ）complex with sulfonate terminated polystyrenes.The resulting SBCs can self-assemble into vesicles,which further show a spontaneous fusion with an hour-scale fusion time in chloroform-methanol（v/v=1）mixed solvents.With this much longer fusion process,a series of vesicle fusion intermediates including docking vesicles,arrowlike protrusions,stalk-like intermediates,hemifusion diaphragms and fusion pores,were clearly captured by TEM imaging.It should be highlighted that the fusion processes of SBCs are proposed to be driven by the weak Pt???Pt andπ-πstacking interactions between[Pt（Me₂bzimpy）Cl]⁺cations in the vesicles.This is in sharp contrast to fusion processes induced by hydrogen bonding,metal ion coordination,chemical reaction,and host-guest recognition2.We have successfully synthesized and characterized two classes of star polystyrenes end functionalized with planar platinum（Ⅱ）complexes,SS_nPt-I and SS_nPt-II through coordinating reactions of K₂PtCl₄ with the corresponding star ligands.The resultant star polymers show characteristic spectral and luminescence properties of the platinum（Ⅱ）complexes.The phosphorescence emissions of ³MMLCT transitions are remarkably enhanced in the solvents of weakened quality,i.e.,in the toluene/n-hexane or chloroform/n-hexane mixture solvents with increasing n-hexane content.Here,n-Hexane is a poor solvent of both the polystyrene and planar platinum（Ⅱ）blocks.Of note is that such an AEE feature is evoked in the solutions of the star-like polymers with weakening solvent quality and originates from Pt???Pt andπ-πstacking interactions between the planar platinum（Ⅱ）blocks.Furthermore,these star polymers self-assemble to form unimolecular micelles with a corona of the planar platinum（Ⅱ）blocks and a core of star polystyrenes in the chloroform/methanol mixture solvent with a methanol volume ratio of 90%.In this case,methanol is a selective solvent of the planar platinum（Ⅱ）blocks.3.We have synthesized and characterized two classes of star polystyrenes end functionalized with polyoxometalates,SS_n-POM-1 and SS_n-POM-2 through click reactions of L-1 or L-2 with the corresponding SS_nN₃.These polyoxometalate-polymer hybrid polymers can be directly imaged from DMF dilute solution by TEM measurements.