Synthesis Of Poly(Ethylene Glycol) Modified 2,6-Bis(Benzimidazol-2?-yl) Pyridine Platinum(?) Complexes And Their Controllable Self-Assembly In Solution

Square-planar platinum???complexes can self-assemble into highly ordered structures via Pt???Pt and/or?-?stacking interactions,which result in the presence of metal-metal-ligand charge transition excited states and excimeric excited states,respectively.Platinum???complexes exhibit strong triplet luminescence behaviors in solution,thin film,and solid states,such as long lifetimes in the microsecond range,high quantum yields,and controllable excited state properties.Nowadays,scientists were able to design and synthesize novel platinum???complexes with characteristic luminescence and controllable self-assembly.On the other hand,in the selective solvent,amphiphilic block copolymers,driven by the action of hydrophobicity,can aggregate hydrophobic chains to form micellar cores,while hydrophilic chains creat a corona to colloidally stabilize the micellar cores in the form of solvation.The aggregation morphology of amphiphilic block copolymers is mainly affected by volume ratios,incompatibility,and solvent quality.On the basis of these collective studies,we combine biocompatible poly?ethylene glycol?s?PEGs?with highly luminescent platinum???complexes to synthesize a series of PEG-platinum???metallopolymers.The luminescent properties and self-assembled behaviors of the resuling metallopolymers are investigated systematically.The details are addressed as follows:1.To design and synthesize a range of amphiphilic telechelic metallopolymers with water soluble PEG central chains and hydrophobic platinum???complexes as terminal blocks for the first time.This class of telechelic polymers can self-assemble in water to form vesicular structures.The hydrophobic platinum???complexes at both ends are connected to the same vesicle wall in a slipped stacking model,and the hydrophilic PEG central chains are bent to form the corresponding ring-like coronas.This is a typical flower-like vesicle structure.It should be highlighted that for the first time,flower-like vesicles have been observed for amphiphilic telechelic polymers.Both MMLCT absorption and ³MMLCT emission bands are greatly enhanced.Further wide angle x-ray scattering?WAXS?investigations,together with the aforementioned spectral data,suggest that the flower vesicles are presumably due to Pt???Pt and?-?stacking interactions between the planar platinum???complexes and the hydrophobic effect between the alkyl chains.Upon annealing the aqueous solution by heating,the original nano-sized vesicles are transformed to form thermodynamically stable,giant flower-like vesicles in the micrometric range.To the best of our knowledge,this is the first report of“giant flower-like vesicles”fabricated by telechelic polymers in solution.2.To design and synthesize a series of PEGs mono-functionalized with2,6-bis?benzimidazol-2?-yl?pyridine platinum???complexes.These mono-functional metallopolymers are mixed with the aforementioned telechelic metallopolymers in different molar proportions in water.This is called as the method of“mix and match”.When their mixting ratio is controlled at 1:1,the“mix and match”composite self-assembles to create host-guest nanostructures,where the telechelic metallopolymers self-associate to generate cores for their poor water solubility,while the mono-functional metallopolymers form water soluble corona.The decrease in the mixing ratio to 1:4 leads to the formation of vesicular structures.Meanwhile,the³MMLCT emission band shows clear red-shift,suggestive of enchanced Pt???Pt and?-?stacking interactions during the morphological evolution process.Further solution WAXS characterization points out that the Pt???Pt and?-?stacking interactions between the platinum???complexes played a leading role for the aforementioned morphological evolution and luminescence enhancement.Moreover,these metallopolymers can be utilized as luminescence bio-imaging agents.In several cell toxicity experiments,the metallopolymers exhibit strong cytotoxicity,which may be used as potential chemotherapeutic drugs in tumor treatment.3.To design and synthesize a series of platinum???-containing?,?-telechelic amphiphilic metallopolymers.The A,B,and C blocks are octadecyl and PEG chains and2,6-bis?benzimidazol-2?-yl?pyridine platinum???complexes,respectively.The resulting metallopolymers show remarkable luminescence enhancements in the THF/n-hexane mixture solvents.The mechanism underlying such luminescence enhancements is attributed to the micellelization of the metallopolymers,where the inner micellar cores of the[Pt?bzimpy?Cl]⁺PF₆^-complexes and the outer micellar cores of the PEG blocks are stabilized by the stearyl chains in the dispersions.Accordingly,the aggregation of the[Pt?bzimpy?Cl]⁺PF₆^-complexes into the inner micellar cores further induces the formation of Pt···Pt and/or?–?stacking interactions between the[Pt?bzimpy?Cl]⁺planes.The sequential morphological variations from spheres to cylinders or nanofibers to nanofibers or lamellae coincide well with the increase in the molecular weight of the insoluble PEG block leading to increasing the relative volume fraction of the insoluble blocks.These luminescence metallopolymers show great potential in the fields of nanostructuring fabrication,optoelectronic devices,and chemical sensing.