The Synthesis,Properties And Super Resolution Imaging Of Photoswitchable Fluorescent Polymers Based On Dithienylethenes

Organic photochromic materials have been applied in molecular switches,nano devices and biological imaging and other fields for their special light-response.Among all kinds of organic photochromic compounds,dithienylethenes have been one of the most promising materials,because they have excellent bistable characteristics and fatigue resistance.The fluorescence of photoswitchable fluorescent dithienylethenes can be switched on and off simultaneously with the photochromism.The quick and sensitivive fluorescence detection can present the isomerization of dithienylethenes.However,current photoswitchable fluorescent dithienylethenes can not meet needs of practical applications yet beacause of their hydrophobicity and limited functionality.Photoswitchable fluorescent polymers based on dithienylethenes are promising and have many advantages in practical application.They can be functional conveniently and easy to be controlled with stable performance.Photoswitchable fluorescent polymers based on dithienylethenes have been successfully applied in super resolution imaging.The application of them in super resolution imaging has just started.Introducing photoswitchable fluorescent dithienylethenes in brief and overviewing the demand of probes in super resolution imaging,this dissertation presents several methods to construct photoswitchable fluorescent polymers based on dithienylethenes,studies their photochromic and photoswitchable fluorescence,and explores their applications in super resolution imaging.It mainly comprises four works as the following list:(1)To obtain the amphiphilic and photoswitchable fluorescent polymer based on dithienylethenes,a biocompatible and hydrophilic PEG chain is connected covalently with photoswitchable fluorescent dithienylethenes by the click chemistry.reaction,forming PEG-PMI-DTE with high yield 95%.Upon ultraviolet light irradiation,the conversion efficiencies of PEG-PMI-DTE at photo stationary state(PSS)reaches 98%.PEG-PMI-DTE has a very good solubility in common organic solvents and has a fast response speed with the highest flurescence quenching ratio of 1426.It shows reversibly photochromic and photoswitchable fluorescence upoun the alternate ultraviolet and visible light irradiation with excellent fatigue resistance.All these optical properties benefit the application of PEG-PMI-DTE in super resolution imaging.(2)In order to realize the super resolution imaging of liposomes,stained liposomes are constructed by L-a-phosphatidylcholine,cholesterol,octadecylamine and the amphiphilic and photoswitchable fluorescent polymer based on dithienylethenes PEG-PMI-DTE,using the film dispersion method.The addition of PEG-PMI-DTE have no effect on the critical micelle concertration(CMC)of liposomes with CMC 0.01 mg/mL and 0.0098 mg/mL for the empty and the stained liposomes respectively.Upon ultraviolet light irradiation,the suspension of liposomes stained by PEG-PMI-DTE response fast with the flurescence quenching ratio of 97.Using PEG-PMI-DTE as the probe of super resolution imaging for liposomes,multilamellar vesicles(MLVs),large unilamellar vesicles(LUVs),and small unilamellar vesicles(SUVs)can be observed with the full width at half maximum(FWHM)as low as sub-29 nm.It is the first example of super resolution imaging of liposomes using photoswitchable fluorescent dithienylethenes.(3)In order to solve the problem of water solubility,biocompatibility and specific target,this dissertation designs and synthesizes photoswitchable fluorescent polymers based on dithienylethenes.The styrene derivative containing photoswitchable fluorescent dithienylethenes,isopropyl acrylamide,acrylic ester.containing triphenylphosphonium and chlorine methyl styrene are polymerized through free radical polymerization,forming new and photoswitchable fluorescent polymers based on dithienylethenes.Upon ultraviolet light irradiation,these photoswitchable fluorescent polymers based on dithienylethenes response fast with the fluorescence quantum yield above 0.66.Among them,P4 can be soluble in water at the room temperature with the flurescence quenching ratio of 30.The LCST of P4 is 37℃.Using P4 as the probe of super resolution imaging for mitochondria,the resolution of sub-30 nm is obtained.(4)In order to obtain photoswitchable fluorescent polymers with the end of dithienylethenes,a functional chain transfer agent(CTA)based on photoswitchable fluorescent dithienylethene,DTE-PMI-CTA,is synthesized and applied in the Reversible Addition-Fragmentation Chain Transfer(RAFT)of styrene monomer,getting PS-CTA.Then,polymerization of Poly(ethylene glycol)methacrylate(PEGMA)monomer is conducted using PS-CTA,achieving the amphiphilic block copolymers PS-b-P(PEGMA).The photochromic and photoswitchable fluorescent performance can remain well in DTE-PMI-CTA,PS-CTA and PS-b-P(PEGMA).Upon ultraviolet light irradiation,they have a fast response speed.They show reversible photochromic and photoswitchable fluorescence upoun the alternate ultraviolet and visible light irradiation with excellent fatigue resistance.In toluene,both the fluorescence quantum yields of PS-CTA and PS-b-P(PEGMA)in the open form are 0.74.The flurescence quenching ratio of PS-CTA and PS-b-P(PEGMA)in toluene show 719 and 706 respectively.This provides an effective method to construct photoswitchable fluorescent copolymers with the end of photoswitchable fluorescent dithienylethenes.