Exploration And Performance Research On The Construction Of Unit Of Purely Organic Long Afterglow Material

Ultralong organic room temperature phosphorescent(UORTP)materials are one of the most eye-catching luminescent materials because of their unique advantages such as low cost,low toxicity,adjustable optical properties and stimulus response characteristics.They have increasingly broad application and development prospects in biological imaging,advanced encryption/anti-counterfeiting,sensitive sensors and other fields.In 2020,researchers found an isomer(H-benzo [f] indole,Bd)in the phosphorescent material carbazole.Its content was very small,extremely difficult to separate,but seriously affected the intrinsic properties of phosphorescent.At this time,people realized the importance of the impurity problem,so the impurity problem of phosphorescent materials has become a research hotspot in the past two years.In 2022,Ma Zhiyong’s research group successfully synthesized Bd through a 7-step reaction.Its phosphorescence performance is superior,but the synthesis procedure is too complicated.Therefore,it is necessary to explore the elementary element with similar phosphorescence behavior to Bd to replace Bd to build a new phosphorescence material.In this paper,three novel phosphorescent elements have been discovered and a series of D-A structure derivatives have been synthesized from them.Firstly,their photophysical properties in low temperature toluene solution and low temperature pure powder were studied.Secondly,their ultra-long phosphorescent properties in polymethyl methacrylate(PMMA)and powder substrates were studied.Finally,the organic phosphorescent mechanism involving cationic free radicals was proposed.Specific research contents are as follows:(1)In the second chapter of the thesis,a new class of organic units(N-1and N-2)and their derivatives(PNNA-1 and PNNA-2)with ultralong organic room temperature phosphorescence(UORTP)properties are reported.It is found that the phosphor color can be adjusted in different states or by changing the main substrate.At 77 K,all molecules show a green afterglow in the monomer state and a yellow afterglow in the aggregation state.This is because there is a strong intermolecular interaction in the selfaggregation,which leads to a redshift in the afterglow,and thus presents a multicolor phosphorescence in different states.In addition,PNNA-1 and PNNA-2 exhibit unique photoactivated green UORTP in PMMA films due to the production of their cationic radicals.While PNNA-1@PNCz and PNNA-2@PNCz doped powders show yellow UORTP.In PNCz,cationic free radicals of PNNA-1 and PNNA-2 can exist stably and form strong intermolecular interaction with PNCz,resulting in ultra-long phosphorescent redshift.The result shows a color-adjustable UORTP controlled by the substrate,enabling multi-color phosphorescence controlled by different substrates(PMMA vs.powder).(2)In Chapter 3,we propose a general strategy for constructing UORTP materials from readily available organic units(7H-Benzo [c] carbazole,BCz)to achieve multi-color phosphorescence controlled by different concentrations of a single substrate(contrast between different powders)and ultra-long underwater phosphorescence.When BCz and its derivatives were dispersed into the PMMA polymer matrix,strong(photoactivated)green UORTP were observed from their doping system at room temperature.When they are doped into the powder,the UORTP color can be adjusted between green and yellow depending on the powder substrate and doping concentration in the doping system.Ultralong phosphorescence results from the production of free radical cations.The substrate plays a key role in both stabilizing free radicals and controlling UORTP color.More interestingly,when PMMA is used as the main substrate,the doped films have stronger photoactivated ultralong phosphorescence under water than in room temperature air.BCz not only performs better in ultralong phosphorescent properties than Bd(H-benzo [f] indole),but also in practical applications.This work provides an indepth understanding of the mechanism of UORTP and opens up a new way for the application of organic phosphorescent materials in underwater coating and imaging.In summary,we found three phosphorescent units N-1,N-2 and BCz.These three units and their derivatives(PNNA-1 and PNNA-2,Py Am BCz and CNBr BCz)all have excellent UORTP properties.Compared with Bd(H-benzo [f] indole)and its derivatives reported earlier,the UORTP properties of N-1,N-2,BCz and its derivatives are superior.This study provides another example supporting the possibility that cationic radicals may be a universal mechanism for organic phosphorescence,and we believe that this work could expand the prospects of organic phosphorescence and open up new ideas for the construction of UORTP materials for underwater applications.