Carbonized Polymer Dots And Their Functional Applications

Carbonized polymer dots(CPDs),as a new type of carbon-based nanomaterial,have attracted broad research interest for years,because of their favorable attributes like simple preparation methods,good biocompatibility,unique optical properties,low cost,eco-friendliness.For CPDs,abundant precursors result in their diverse structures and performance,unique polymer characteristics and core-shell structures offer their advantages like functionalization,which all further extend the applications of carbon dots(CDs)in biomedicine,optoelectronic devices,and catalysis,etc.While great progress has been made in the study of CPDs,there are some critical issues yet to be addressed,including the controllable syntheses of multifunctional/high-performance CPDs(e.g.,red/near infrared(NIR)emission,two-photon photoluminescence),the characterization of their fine structures and polymer properties.In this paper,three kind of multifunctional/high-performance CPDs were designed and synthesized from three type of precursors(drug molecules,traditional chinese medicine,and aromatic amines).The relationship between structures and performance,applications in biomedicine and photoelectric display were investigated in detail.There were several critical points of innovation in this paper:CPDs was firstly used to elucidate CDs prepared via“bottom-up”,and their polymer characteristics and core-shell structures were deeply investigeted;bifunctional CPDs(Met-CPDs-250)with blue emissive and selective antibacterial activity were obtained from metronidazole;firstly reported the hepatobiliary system of CDs;prepared CPDs with crossing blood brain barrier for the first time;synthesized deep red emissive CPDs with the full width at half maximum(FWHM)of 20 nm and the photoluminescence quantum yields of 59%.Specifically,three aspects were introduced in detail in this paper.In chapter two,blue emissive CPDs(Met-CPDs-250)with selective antibacterial activity against obligate anaerobes were prepared by hydrothermal treatment of metronidazole,and then used as the model to study the relationship between structures/performance of CPDs and precursors.The formation and fluorescence mechanism of Met-CPDs-250 were investigated by controlling the reaction time and reaction temperature.Met-CPDs-250 behaved the similar antibacterial activity with metronidazole due to their same pharmacophore.Thus,the structures and performance of CPDs were closely related to precursors.More importantly,Met-CPDs-250possessed better biocompability,lower cytotoxicity,higher water-solubility and stability,and excitation-dependent emission,and finally were applied in cell imaging.In chapter three,it is highly desirable and challenging to synthesize high-performance CPDs with red/NIR emission,which always possess large conjugated sp²-domains.And the Met-CPDs-250 model in chaper two presented that the performance of CPDs could be controlled by precursors.Thus in this paper,conjugated compounds with heteroatom-doped heterocyclic/aromatic rings were chosen as precusors to obtain high-performance red/NIR emissive CPDs via the appropriate reaction conditions.Deep red emissive CPDs(TL-CPDs)with narrow FWHM of 20 nm,QY of 59%,and two-photon fluorescence,were made from taxus leaves by the solvothermal method,and purified via silica gel column chromatography in this chapter.Then the unique polymer characteristics and carbon-core structures of CPDs were deeply studied for the first time based on detailed characterizations like transmission electron microscopy(TEM),viscosity.And the fluorescence mechanism of TL-CPDs were investigated through controlled experiments and femtosecond transient absorption(TA)spectroscopy.Due to the low toxicity,high QY,excellent optical properties,good biocompatibility,and strong tissue penetration of TL-CPDs,we developed their applications in one-photon and two-photon bioimaging as well as photoelectric display.Meanwhile,their metabolic pathways were also explored in details.In chapter four,red emissive CPDs(o PD-CPDs-50)with QY of 31%were produced by hydrothermal treatment of o-phenylenediamine with HNO₃.The formation and fluorescence mechanism of o PD-CPDs-50 were explored by adjusting the dosage of HNO₃ before the reaction.Due to their high water dispersibility,low toxicity,high QY,excellent optical properties,good biocompatibility,and strong tissue penetration,,the applications of o PD-CPDs-50 in bioimaging were developed.Meanwhile,new metabolic pathway of CDs was reported for the first time.More importantly,the o PD-CPDs-50 could enter brain when the blood-brain barrier remains intact,which was reported for the first time.Furthermore,combined with biotinylated dextran amine(BDA),o PD-CPDs-50 were applied in anterograde neural tracing.In summary,we named CPDs for the first time,and in view of practicability,three kind of multifunctional/high-performance carbon-based nanomaterials were designed and prepared by controlling the precursors.This paper has presented pioneering work for applications and development of CDs,which is instructive for the controllable syntheses of multifunctional/high-performance of carbon nanomaterials.