Design,Synthesis And Performance Of Pure Organic Room Temperature Phosphorescent Materials Based On Bicarbazopyridine

Phosphorescent material means that the material itself can still emit light for a period of time after the excitation light source is turned off.It has attracted much attention because of its potential applications in optoelectronic equipment,anti-counterfeiting and encryption,biological imaging,and data storage.However,due to the limitations of phosphorescent materials.For example,there are very few organic phosphorescent materials with aggregation-induced emission enhancement(AIEE).Organic phosphorescent materials often require ultraviolet light to activate the phosphorescence of the materials,which greatly limits the practical application of organic phosphorescent materials.At present,phosphorescent materials Afterglow colors have covered the full spectrum,but white afterglow phosphorescent materials are very rare.Therefore,it is of great significance to develop and explore phosphorescent materials with aggregation-induced emission enhancement,white afterglow,and visible light excitation properties.In this paper,carbazole is used as electron donor,pyridine ring,cyano group and amide group are used as electron acceptor.Cyano group and amide group can promote intersystem crossing(ISC).Based on this,we designed and synthesized D-A-D structure of pure organic room temperature phosphorescent material,by adjusting the difference of the substituent and the substitution position of the substituent,this unique design concept realizes the organic room temperature phosphorescent material with specific properties.The main content of this paper is divided into the following three parts.1.The afterglow colors of phosphorescent materials with carbazole groups are usually yellow and red.Single-component pure organic white afterglow materials are very rare.In the second chapter of the paper,we attached two carbazoles at the meta position of the pyridine ring.At the same time,the pseudo-halogen cyano-CN is introduced into the leading position to obtain the molecule oDCzPyCN.The cyano group can promote ISC and generate more triplet excitons.After the UV lamp is turned off,oDCzPyCN exhibits a white afterglow at room temperature.The white afterglow of oDCzPyCN is made up of thermally activated delayed fluorescence(TADF)(455 nm,～90 ms)and organic ultralong phosphorescence(OURTP)from the intermolecular interaction-stabilized triplet state(T1*)(542 nm and 592 nm,～240 ms).The thermally activated delayed phosphorescence(TADP)from T1 is negligible.2.The excitation of phosphorescent materials often requires ultraviolet light,but ultraviolet light has greater phototoxicity to organisms,which limits the practical application of materials.Visible light has stronger penetrability for biological analysis and biological imaging.In the third chapter of the thesis,we hydrolyzed the cyano group to the amide group based on the second chapter,and obtained the new molecule oDCzPyCO.Since the ketone carbonyl structure has abundant lone pairs of electrons,the S1 is mainly composed of(n,π*)and Tn is mainly composed of 3(π,π*),which can increase the spin-orbit coupling(SOC),thereby increasing the ISC.Not only ultraviolet light can excite afterglow,but also mobile phone LED lights can also excite afterglow.Not only ultraviolet light can excite afterglow,but cell phone LED lights can also excite afterglow.After turning off the light source,a green afterglow visible to the naked eye can be observed,and the life span reaches about 340 ms.There is a clear overlap between the excitation spectrum of oDCzPyCO at 547 nm and the emission spectrum of the LED,which proves that it can be excited by visible light.3.Carbazole itself has no AIEE properties.In Chapter 4 of the paper,we changed the substitution position of the amide group to the para position of the pyridine ring on the basis of Chapter 3.The resulting organic small molecule pDCzPyCO has both AIEE and ultra-long organic phosphorescence,emits blue fluorescence under 365 nm ultraviolet light.After the UV lamp is turned off,a continuous yellow afterglow can be observed at room temperature,with a lifespan of up to about 580 ms.At the same time,in the tetrahydrofuran/water system solution ofpDCzPyCO,as the water content increases from 0%to 95%,the luminescence of the solution is significantly enhanced under 365 nm light.Experimental and theoretical studies have shown that as the water content increases,molecules gradually aggregate,and the two carbazole twisted structures form a crowded conformation.Intramolecular charge transfer(ICT)leads to AIEE.Through such a unique D-A-D structure,a series of organic phosphorescent small molecules with special properties have been obtained.