Constructiion Of Carbon Dots And Their Luminescence Regulation

Carbon dots(CDs)is an emerging zero-dimensional carbon nanomaterial with strong potential for applications in photoluminescence,bioimaging and optoelectronic devices due to their simple preparation process,wide source of precursors and unique optical properties,good biocompatibility,electronic properties and environmental friendliness.However,the photoluminescence mechanism of carbon dots is still unclear due to the complex structure of their precursors and the difficulty in tracking the changes involved in the carbonisation process,which further hinders their industrialisation.How to modulate the photoluminescence properties of carbon dots,including long wavelength luminescence with high quantum yields and overcoming the aggregation-induced burst effect to obtain solid-state luminescence,especially with room temperature phosphorescence properties,are hot issues that need to be addressed.In response to the above problems,this thesis focuses on the direction of modulating the long-wavelength emission and solid-state luminescence of carbon dots,as follows:1.Study on the construction and properties of red carbon dots from ophenylenediamine.Most of the carbon dots reported so far are excitation wavelength dependence and their emission wavelengths are mostly concentrated in the blue to green region,making them difficult to reach the long wavelength emission region.Short-wavelength radiation causes significant interference with the background radiation of biological tissues,which significantly reduces the penetration depth of carbon dots for bioimaging and light-mediated therapy,and most carbon dots decrease their emission intensity with increasing excitation wavelength in the long-wavelength region,which greatly limits the application of carbon dots in bioimaging.By introducing terephthalic acid(TA)into the reaction used o-phenylenediamine(o PD)as a precursor for the preparation of green luminescent carbon dots and modulating their surface,deep-red fluorescent carbon dots with high quantum yields at independent excitation wavelengths and increasing emission intensity with increasing excitation wavelengths were obtained.By analyzing their structural and optical properties,a structural strategy for the preparation of red-emitting carbon dots using the terephthalic acid type as a precursor is proposed,which is the construction of a donor-acceptor conjugation strategy.2.Study on the construction and application of multi-colour afterglow solid-state luminescent carbon dots.Dispersing carbon dots into a matrix is a common method to overcome aggregation-induced quenching.Since cyanuric acid(CA)is a good hydrogen bond acceptor and donor,the hydrogen bonds formed between the matrix and the carbon dots can not only effectively stabilize the excited triplet state and obtain room temperature phosphorescence,but also have a very high stability to effectively prevent oxygen burst excitons in air and water,realising the inextinguishability of phosphorescence in water,and obtaining a three-mode luminescence solid CDs-matrix composite with fluorescence,room temperature phosphorescence and delayed fluorescence.In order to demonstrate the universality of this method,different types of carbon dots were chosen and different types of carbon dot-based composites were prepared,which were successfully applied in the field of anti-counterfeiting by exploiting the differences in their lifetimes.3.Study on the construction of matrix free solid luminescent carbon dots.Pentasodium diethylenetriaminepentaacetate(DTPA-Na)and Glycine(Gly)were used as precursors,matrix-free solid carbon dots with ultra-high fluorescence quantum yield(21.6%)and green room temperature phosphorescence were synthesized.The carboxyl groups and amino groups between the precursors are dehydrated and condensed to form amides,which eventually form dendritic polymer structure speculations.Room temperature phosphorescence may come from the rich nitrogen-containing or oxygen-containing functional groups on the surface of the polymer chain,and the hydrogen bonds formed between the long chains also effectively inhibit the quenching of excitation triplet excitons and stabilize the emission of room temperature phosphorescence.