Preparation And Anti-counterfeiting Applications Of Long-lived Phosphorescent Carbonized Polymer Dots

Room temperature phosphorescent(RTP)materials have received tremendous interest in the past few years because their unique single-triplet transition processes and the resultant long-lived luminescence offer unique opportunities toward various applications ranging from optoelectronic devices,bioimaging,to information security.However,the research of room temperature phosphorescent materials still faces great challenges due to the spin-forbidden barrier of triplet excitonic transitions.At present,room temperature phosphorescent materials are mainly limited to organometallic complexes,and a few are pure metal-free organic compounds.However,organometallic complexes have disadvantages such as high cost,strong toxicity,and complicated preparation process.Pure organic compounds have disadvantages such as high enviro nmental requirements for preparation,and their luminescence is greatly affected by temperature,and their emission lifetimes are also short.It often takes tens of milliseconds to identify long afterglow luminescence in the real applications,so this fast decay is difficult to apply in the field of anti-counterfeiting.Carbon dots(CDs),as a new type of nanoscaled optical materials,have received extensive attention from researchers in recent years.Carbon dots usually refer to carbon nanoparticles with a size less than 10 nm,which are composed of sp~2/sp~3 hybrid carbon cores and abundant functional groups or polymer chains on the surface.Due to their high quantum yield,tunable emission wavelength,low cost,environmental friendliness and easy functionalization,carbon dots possess the prospect as a new generation of RTP materials.Based on the background mentioned above,herein we investigate the preparation and anti-counterfeiting applications of long-lived phosphorescent carbonized polymer dots.The main research contents are summarized below:(1)Long-lived room temperature phosphorescence emission based on carbonized polymer dots by doping heteroatomsIn this study,room temperature phosphorescent carbon dots with self-protected structures were realized by incorporating heteroatoms into carbonized polymer dots.The work in this study can achieve phosphorescence without matrix encapsulation.On the one hand,excited states can be effectively self-fixed through carbonized polymer dots with a cross-linked polymer/carbon skeleton structure.Through covalent bonding emission center and blocking the movement of the polymer chains,the quenching of room temperature phosphorescence can be suppressed.On the other hand,the intersystem crossing of electrons can be promoted by doping heteroatoms to improve the spin-orbit coupling between triplet states,thus realizing the long-lived phosphorescent emission.We exploit the properties of this ultra-long-lived room temperature phosphorescence for a range of anti-counterfeiting printing applications.(2)Tuning the wide-range phosphorescence lifetime by adjusting the stability of the self-protected structure of carbonized polymer dotsWe achieved a wide range of lifetime regulation by adjusting the amount of phosphoric acid added.Increasing the amount of phosphoric acid added can increase the content of polymer chains on the surface of the carbonized polymer dots.The increase of polymer chains can make the carbonized polymer dots aggregate continuously by intertwining with each other,and the aggregation of the carbonized polymer dots will make the structure become more and more stable,which leads to the enhancement of phosphorescence emission,which in turn enables wide-range phosphorescence lifetime tuning.We exploit this wide-lifetime tunable room-temperature phosphorescence for multi-layered anti-counterfeiting printing applications.(3)Thermally driven amorphous/crystalline phase transformation to synthesize multicolor phosphorescent carbonized polymer dotsWe propose a strategy to prepare thermally responsive carbonized polymer dots with multicolor long-lived room temperature phosphorescence by varying the heating temperature.A red-shift of the room-temperature phosphorescence emission wavelength was achieved by an external heating stimulus.With the increase of temperature,the carbonization degree of carbonized polymer dots increases,the carbonized polymer dots transform from amorphous to crystalline state,and the degree of conjugation of crystalline carbon cores increases,resulting in the decrease of the band gap of excited state to triplet state,and the red-shift of the emission wavelength is obtained.We utilize this multicolored room temperature phosphorescent carbonized polymer dots for temperature-controlled anti-counterfeiting applications.