| Carbon-based nanodots(CDs)are a new kind of carbon-based nanomaterials with fluorescence properties.Due to their excellent optical properties,good photostability,and ease to functionalize on the surface,CDs have been widely applied in many yields,such as cell imaging,cancer therapy,photocatalysis,biosensing et al.However,the critical factors which limit the development of CDs in other yields are 1.The unclear fluorescence origin of CDs.2.The unsuitable purification measurement.3.The ambiguous chemical structures of CDs.The unclear fluorescence mechanism of CDs caused the precursors in the preparation of CDs with specific fluorescence to be constant.While unsuitable purification would lead to a large loss of products.And the ambiguous chemical structures eventually resulted in the limitation of functional modification and made the large-scale preparation of CDs difficult.In this dissertation,we prepared CDs with multi-color emission by hydrothermal or solvothermal method from phenylenediamine.By carefully analyzing the chemical structures and fluorescent behaviors of CDs,we have explored the fluorescence mechanism and formation mechanism of CDs.Besides that,we also expanded the application of prepared CDs in the LEDs industry,polyphenol detection,cell imaging,and other yields.The details are as follows:1.With the solvothermal method from 1,2-phenylenediamine,we prepared o-pd CDs with yellow emission.After purification by column chromatography,two kinds of molecular fluorophores named 2,3-diaminophenazine(DAP)and 2-amino-3hyroxyphenazine(AHP)were identified by HPLC-MS,NMR spectra,and FTIR spectra et al.We also have separated two kinds of compounds with green emission(G-CD 1 and G-CD 2)and a kind of compound with blue emission named B-CD.By comparing the fluorescent behaviors of DAP with o-pd CDs,we confirmed that the fluorescence of o-pd CDs originated from the synergistic effect of molecular states,surface states and carbon core states.And the molecular state from DAP is the main contributor to emission.Moreover,by analyzing the components of o-pd CDs,we speculated that the o-pd CDs were formed from DAP,which aggregated,carbonized,and collapsed under solvothermal reaction.Finally,we mixed DAP,G-CD and B-CD with PVP to prepare multi-color and white color fluorescent powders.Based on this,we have prepared multi-color LEDs and W-LEDs.The CRI of prepared W-LEDs was as high as 87.Because multi-color LEDs and W-LEDs play an important role in medical fields such as wound healing and skin anti-inflammatory,our works expanded the application of CDs in the LEDs industry and also could provide a reliable theoretical basis for the preparation of CDs from 1,2-phenylenediamine.2.Based on the study about the fluorescence mechanism of o-pd CDs.The red emissive CDs(R-CDs)with an absolute quantum yield of 16.67%were prepared by solvothermal method from 4-chloro-1,2-diaminobenzene.Further experiments confirmed that 4-chloro-1,2-diaminobenzene could easily dechlorinate under the action of H+,and eventually formed molecular fluorophore 5,14-dihydro-5,7,12,14tetraazapentacene derivate.Moreover,we have designed fluorescent sensors for the detection of tea polyphenols based on the inner filter effect(IFE)and static quenching mechanism.The results suggested that the fluorescence quenching curves of R-CDs had a good linear relationship with the concentration of tea polyphenols.And the LOD was as low as 68 ng/mL.Finally,R-CDs were successfully applied in labeling lysosomes of HeLa cells due to the pretty high quantum yield and good biocompatibility.In cell imaging,the signal of R-CDs had a large overlap with Lyso-Tracker Green(Commercial dyes),and the PCC was as high as 0.91.Suggesting that R-CDs have great potential application in this field.3.Because 1,3-Phenylenediamine possess specific advantages in preparing CDs with high quantum yield,we have carefully studied its origin of fluorescence.By column chromatography,we have separated a component named M-CD with an absolute quantum yield of 64.20%from M-CDs,which were prepared by 1,3phenylenediamine and HCl.And by using HPLC-MS,NMR spectra,and UV-vis absorption spectra,we have confirmed that M-CD consisted of molecular fluorophores N1,N3-diethylbenzene-1,3-diamine and their derivates.The results suggested that the fluorescence of M-CDs originated from molecular states.In cell imaging,no matter in living cells or fixed cells,M-CD both exhibited wonderful nuclear targeting in HeLa cells,which is the first reported.Further experiments and a macromolecular docking model indicated that the N1,N3-diethylbenzene-1,3-diamine group could bind to the DNA double helix structure with high stability and eventually endowed M-CD with wonderful nuclear targeting.All of the above suggest that M-CDs have great potential application in cell imaging. |
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