Room Temperature Phosphorescent Carbonized Polymer Dots And Their Applications

Room temperature phosphorescence(RTP)attracts broad attentions and tremendous interest from researchers because of its long afterglow,large Stokes shift and highly environmental sensitivity.Conventional room temperature phosphorescent materials include inorganic complexes,organic metal complexes and pure organic composites,which are complex to synthesize,expensive,highly cytotoxic and not environmental-friendly.Therefore,it is necessary to develop environmental-friendly,facile and low-cost materials.Carbon dots(CDs),as new kind of carbon-based luminescent nanomaterials,have attracted extensive attentions from researchers in recent years due to their good biocompatibility,environmental friendliness,low cost and convenient preparation.Carbonized polymer dots(CPDs),as one kind of CDs,which have the advantages of both polymer and quantum dots,and have great application potential.In the past few years,a lot of room temperature phosphorescent CPDs have been developed and applied in the field of security,information encryption,sensing and biological imaging,etc.However,the early developed room temperature phosphorescent CPDs show low brightness,poor humidity resistance and single phosphorescent color.In this paper,three CPDs or their derivative materials were designed and synthesized based on similar types of precursors(nitrosilane and phosphoric acid),and applied in the fields of anti-counterfeiting,information encryption and biological imaging.The innovation of this paper lies in the introduction of three dimensional hydrophilic silica covalent cross-linking network,which perfectly fits crosslink-enhanced emission effect(CEEE)and achieves the restriction and protection of luminescent units.We first made solid room temperature phosphorescent CPDs for information encryption and graphics security;And then the solid room temperature phosphorescent CPDs coated with hydrophilic silica shell in water,so that the phosphorescence of CPDs will not be quenched by the quenching factor in aqueous solution,and then CPDs can be used in biological imaging;Finally,we also made CPDs with multicolor RTP for graphic anti-counterfeiting.In detail,the work of this paper can be summarized as the following three contents:In chapter 2,long lifetime solid room temperature phosphorescent CPDs were prepared by one-step microwave assisted heating of 3-(2-aminoethylamine)propyl dimethoxymethyl silane and phosphoric acid aqueous solution raw materials.After ceasing excitation light,the obtained CPDs can exhibit bright yellow-green RTP with absolute photoluminescence quantum yield of 34.17%,absolute phosphorescence quantum yield of 11.42% and long lifetime of 1420 ms,which lasts for about 16 s to the naked eyes.The corresponding CPDs were synthesized under different microwave reaction time,and formation process of room temperature phosphorescent CPDs were investigated.3-(2-aminoethylamine)propyl dimethoxymethyl silane was replaced by another silane coupling agent with similar structure and composition for comparison.The new CPDs for comparation were prepared and their phosphorescence properties at room temperature were analyzed in detail.It can be said that both the precursor molecule and the reaction time have an important effect on the RTP of the CPDs.Finally,we apply the obtained CPDs into information encryption and polyethylene terephthalate(PET)film graphic anti-counterfeiting with facile way.In chapter 3,we covered the long lifetime solid room temperature phosphorescent CPDs obtained in chapter 2 with three dimensional hydrophilic silica covalent cross-linking network and obtained ultra-long lifetime aqueous room temperature phosphorescent CPDs composites.The encapsulation of three dimensional hydrophilic silica covalent cross-linking network ensures the aqueous solubility of the CPDs composites while isolating from the surrounding oxygen and other substances that have quenching factors in aqueous solution.In addition,the encapsulation of three dimensional hydrophilic silica covalent cross-linking network also limits the vibrational motion of the relevant luminescent units of the CPDs,reduces the non-radiative inactivation rate of the triplet excitons,and achieves high quantum yield phosphorescent emission of the CPDs composites in aqueous solution.The obtained aqueous CPDs composites exhibit bright aqueous RTP with absolute photoluminescence quantum yield(QY)of 12.61%,absolute QY of 5.08% and RTP lifetime of 1460 ms,which lasts for about 10 s to the naked eyes.The RTP CPDs composites aqueous solution is nontoxic and biocompatible.These brilliant characteristics allow CPDs composites aqueous solution to be applicable in biological imaging.After cytotoxicity and p H stability tests,the aqueous room temperature phosphorescent CPDs composites were applied in vivo and in vitro biological imaging.In chapter 4,1-[3-(trimethoxysilane)propyl] urea and phosphoric acid were selected as precursors,and the N,P co-doped CPDs with multi-color were prepared by one-step microwave assisted heating method under different reaction time.With the increase of microwave reaction time,the RTP color of the CPDs gradually changed from yellow to blue,the emission wavelength of RTP gradually shifted from long wavelength to short wavelength.The maximum absolute phosphorescent quantum yield of the CPDs is 59.41%(yellow phosphorescent CPDs),the lifetime is1065 ms,and the afterglow of all obtained CPDs can be more than 5 s.Because of the existence of multiple emission units,the photoluminescence of CPDs shows excitation dependence.The reason why the RTP color of CPDs showed a gradual blueshift was the decrease of C═O as the extension of microwave reaction time.In view of their fascinating multicolor RTP properties,potential applications of CPDs in the field of anti-counterfeiting painting were presented.This work would inspire further detection of other researchers to multicolor afterglow materials.In summary,we designed and synthesized three excellent room temperature phosphorescent CPDs or their derivative materials through the selection of precursor molecules,regulation of reaction conditions and post-treatment of reaction products.Our work has reference significance for the design and synthesis of phosphorescent CPDs at room temperature.