Design And Synthesis Of Pure Organic Room Temperature Phosphorescent Materials And Their Applications In Anti-counterfeiting

Pure organic room-temperature phosphorescence(RTP)materials have shown important application prospects in optoelectronic devices,anti-counterfeiting,bioimaging and so on because of their advantages of low toxicity,low pollution,good biocompatibility and easy coordination of structure.However,pure organic room temperature phosphorescent materials can only be observed in low temperature or inert gas environment because of their low spin orbit coupling,spin resistance from singlet to triplet state,easy deactivation of triplet state and easy quenching by oxygen.How to construct pure organic room-temperature phosphorescence materials has become a hot topic in recent years.Organic room-temperature phosphorescence molecules can be constructed by enhancing spin-orbit coupling to produce effective ISC and inhibiting non-radiation attenuation;in addition,free radical-ion pair,lone pair electron,heavy atom effect,crystallization induced phosphorescence and other methods can be used to design room-temperature phosphorescent molecules.However,so far,the design of organic materials with high phosphorescence efficiency and ultralong lifetime is still a great challenge.The research work on high efficiency and ultra-long organic room temperature phosphorescent materials is still relatively few,and there are still many difficulties.In this paper,we propose a new method to design high efficiency ultralong room-temperature phosphorescence materials,using carbazole,(Triphenylphosphoranylidene)acetaldehyde as donor groups,on the basis of which halogenated benzylbenzene,malonitrile are introduced,pure organic molecules were designed to present RTP.Among them,halogenated N-benzylcarbazole derivatives exhibit different photophysical properties in different physical states,and the quantum yield of phosphorescence can be as high as 38% in cluster state,which shows a good application prospect in data encryption and anti-counterfeiting application.The long afterglow from yellow to red is regulated by changing donor and acceptor groups.The following are the main contents of this study:(1)carbazole is used as the parent to synthesize 9-(4-flubenzyl)-9H-carbazole(FBC),9-(4-chlorobenzyl)-9H-carbazole(CBC),9-(4-bromobenzyl)-9H-carbazole(BBC),9-(4-iodobenzyl)-9H-carbazole(IBC)four room-temperature phosphorescence molecules.To achieve efficient room-temperature phosphorescence of organic materials with ultralong lifetime,it is imperative to resolve the dilemma that the introduction of heavy atoms simultaneously improves emission efficiencies and shortens the emission lifetimes.Herein,we report a new molecular design approach for halogenated luminogens with a methylene bridge to avoid the lifetime shortening induced by heavy halogens and propose a general molecular engineering strategy to realize efficient and ultralong room-temperature phosphorescence via halogen-mediated molecular clustering.The halogenated N-benzylcarbazole derivatives show distinct photophysical behaviors depending on different physical states,including single-molecule state and cluster state.Their crystals demonstrate the halogen-dependent emission duration of RTP upon excitation.Experimental data and theoretical analysis indicate that halogen-regulated molecular clustering in the crystal is responsible for the generation of efficient ultralong RTP,and halogen-dominated molecular engineering favors the promotion of the intersystem crossing process and the following triplet emissions.(2)Condensation of(Triphenylphosphoranylidene)acetaldehyde with malonitrile is carried out to design the D-?-A structure.The target molecule has different optical properties in different physical states.At room temperature,weak fluorescence is emitted in the solution and powder states,while in the crystal state,when the ultraviolet lamp is turned off,the bright red afterglow is visible to the naked eye.On the basis of phosphorescent molecules,an electron-withdrawing group is introduced to obtain a red long afterglow luminescent material with high quantum yield,which realizes the regulation from phosphorescent molecules to red long afterglow materials with high quantum yield.In summary,we designed and synthesized a series of RTP materials and further applied them to encryption and anti-counterfeiting,etc.First,the molecules of halogenated benzylbenzene were introduced into the carbazole group to obtain the yellow long afterglow with high quantum efficiency and applied to anti-counterfeiting and encryption using the long-life properties of their RTP.Moreover,using the malonitrile group as the acceptor,D-?-A structure was designed,the compound TPEM was synthesized,and the photophysical and chemical properties were studied.At room temperature,the crystal shows high quantum efficiency red RTP,and has been successfully applied to anti-counterfeiting applications.