Preparation,Fluorescence Properties And Applications Of Novel Nitrogen-doped Carbon Dots Derived From Aphen

In recent years,carbon dots(CDs)have been widely used in many fields such as biological imaging,full-color displays and light emitting diodes(LEDs)due to their excellent luminescence properties,low toxicity and low cost,etc.In these areas,one of the main problems of the CDs is it can hardly achieve high fluorescent quantum yield(QY),especially with long-wavelength emission,which will limit their broader applications.To enhance the fluorescent QY,great efforts have been made to optimum the experimental conditions and a lot of materials have been used as reactants for the synthesis of CDs.Previous studies showed that the QY could be significantly improved through introducing nitrogen,phosphorus,sulfur,boron and other elements into the CDs.It is worth noting that acquiring long-wavelength and multicolor emission colors of CDs is still very difficult,some researchers also used surface state and size control,solvatochromic effect,heteroatom doping and energy transfer to obtain the CDs with long-wavelength and multicolor emission.In addition,CDs-based white light-emitting materials have gained heightened attention recently due to their extensive applications in the fields of lighting and displays.However,it should be a greater technological challenge to realize bright white-light emission from a single carbon dot.Due to the need for cumbersome sample pretreatment,expensive instrumentation,fine operation,and professional operators,some traditional laboratory instruments are not competent for on-site analytical determination,thus,designing new portable sensors is imminent.In the field of biomedicine,the changes in intracellular pH also play an important role in pathological processes and various physiological,such as early cancer formations and regulating cell behaviors.However,fluorescent probes are used to detect actual intracellular pH,the change in fluorescence intensity may be affected by many parameters,such as the cytotoxicity of the probe itself,the bleaching of the dyes,and the solubility and biocompatibility of the sample in biological systems.It is well known that CDs with longer wavelength emission are particularly important for biological imaging because red and near-infrared wavelengths can penetrate deeply into tissues without damaging the body.In addition,the multi-color luminescent probe can avoid the harm caused by the fluorescent internal standard and protein fluorescence interference.Therefore,in order to achieve long-wavelength emission fluorescent probe,especially overcome the above detection limitations of intracellular pH,especially the synthesis of environmentally friendly multifunctional carbon dots and their application in multi-color biological imaging is still a huge challenge.In this thesis,a series of research work on the synthesis and application of carbon dots with special structure and optical properties has been carried out mainly by using a nitrogen-containing heterocyclicAphen as a carbon source.We systematically studied the physicochemical properties and luminescence mechanism of the synthesized carbon dots,and applied carbon dots to construct white LED and new fluorescent pH test paper,and finally extended them to intracellular pH detection and cell imaging.Our work mainly includes the following two parts:In the first section,we have developed a novel strategy to fabricate the nitrogen doped multiple-cores@shell structured CDs with controllable fluorescence by a facile one-pot hydrothermal method using 1,10-phenanthrolin-5-amine(Aphen)and citric acid(CA)as carbon sources.The special multiple-cores@shell structure can endow the CDs with the tricolor emission bands including blue,green and red fluorescence,and we explored the origin and mechanism of the triple emissions from the CDs.Moreover,there is an obvious concentration effect for the CDs,and the red emission of CDs obviously increases as their concentration increases,and the maximum QY can reach 67 % which is the highest value reported for red-emitting CDs at 630 nm.By adjusting the excitation and concentration of multiple-cores@shell structured CDs,we can also realize a pure white emission of single carbon dot with a QY of 29 % which is the highest QY yet reported for pure white-light emission from single CD.In addition,the as-prepared multiple-cores@shell structured CDs can be used to fabricate white LED device with a variety of excellent properties such as good anti-photobleaching and temperature stability.In the second section,based on the the unique structural features of Aphen moieties from the surface of above prepared multiple-cores@shell structuredCDs,the fluorescence emission bands of the CDs may be effectively regulated and further display an interesting pH dependence through optimizing the experimental condition.Inspired by this idea,herein,we proposed a facile means for preparing new type of fluorescent pH test paper which can qualitatively and quantitatively analyze the pH of water in solution,in biological media,and even in nature,through dosesensitive color changes.At the same time,with the low cytotoxicity,good biocompatibility,and extraordinary photostability,CDs were also applied into intracellular pH detection and cell imaging.In addition,the multi-core-shell structures endow the CDs with multi-color emission characteristics,providing a new platform for sensing of intracellular pH by cellular imaging.