Stimuli-Responsive Carbonized Polymer Dots And Their Composites:Synthesis And Their Application

Carbon dots are fluorescent materials with a diameter of 20 nm or less.They usually posses sp~2 and sp~3 hybrid carbon skeletons inside,and a lot of chemical groups on the surface.Carbon dots can be synthesized from lots of materials via different methods.Thus,carbon dots can be divided into many types.In this paper,the carbonized polymer dots are mainly discussed.Carbonized polymer dots are a major class of carbon dots that combine the characteristics of nanoparticles and polymers.They are mainly prepared by the bottom-up method.The reactants suffered dehydration,cross-linking and further carbonization before they became carbonized polymer dots.Compared with traditional fluorescent materials,they possess outstanding advantages such as high PLQY,good water solubility,resistance to photobleaching,low cost,environment friendly and good biocompatibility.As an emerging fluorescent material,they have been widely applied in bioimaging,nanomedicine,anti-counterfeiting,sensors,catalysis,photovoltaic devices etc.However,the real application of carbonized polymer dots is still on early stage.In order to satisfy the needs of practical applications,the carbonized polymer dots and their composites with stimuli responsive properties are synthesized and applied in areas such as bioimaging and temperature monitoring.In the second chapter,we synthesized a kind of acidophilic red/blue dual-emission carbonized polymer dots with tryptophan and o-phenylenediamine.With different synthesis conditions,red and blue fluorescent carbonized polymer dots were synthesized,respectively.The carbonized polymer dots with red emission have an emission peak at 620 nm with a PLQY of 24.33%.The synthesized carbonized polymer dots can be applied as a conversion layer in the fabrication of LED.In addition,based on their acidophilic and dual-emission properties,this type of carbonized polymer dots can be used not only as a fluorescent probe,but also as a novel detection probe for distinguishing different bacteria,including Porphyromonas gingivalis,Streptococcus mutans,Escherichia coli and Staphylococcus aureus.In the third chapter,we synthesized a new type of carbonized polymer dots with citric acid and o-phenylenediamine.The synthesized carbonized polymer dots aggregated in a neutral aqueous solution leading to an obvious fluorescence quenching.While they could well disperse in acidic and alkaline solutions with stable fluorescence.In this chapter,we confirmed the contribution of organic fluorescent molecule molecules to PLQY.And based on the fluorescence-pH dependent property of carbonized polymer dots,we have achieved selective imaging of lysosomes with non-targeted carbonized polymer dots for the first time.They can also be used to monitor the intracellular pH variation during apoptosis.Different from other organic dyes or carbonized polymer dots,the carbonized polymer dots in this work have a fluorescence-enhancement effect in living cells under confocal fluorescent microscopy and are ideal imaging agents for long-term cell monitoring.In the fourth chapter,to endow a non-sensitive carbonized polymer dots with a targeted and sensitive response signal for given stimuli,we could combine them with stimuli-responsive polymers.Herein,we combine a highly fluorescent carbonized polymer dots synthesized from citric acid and ethylenediamine with a thermal responsive polymer,PNIPAM,to obtain a temperature-responsive carbonized polymer dots composite.With the self-quenching effect of the carbonized polymer dots at high concentration and the volume variation of PNIPAM at different temperature,the concentration of carbonized polymer dots in the composite varies,leading to the PL intensity decrease or increase.The prepared temperature-responsive composites have excellent reversibility,and the PL intensity variation could be detected with naked eye.