Synthesis And Properties Of Pyromellitic Diimides Fluorescent Materials With AIE Properties

For many years,organic fluorescent materials have been attracting attention due to their potential applications in organic light-emitting diodes,biological imaging,optoelectronic devices and sensors.However,most of the conventional organic luminophores always shown strongly fluorescence emission in the dilute solution and exhibited non-emission in their aggregated stated and solid state,which called the infamous aggregation-caused quenching(ACQ).Fortunately,in 2001,an unusual luminescent material with the aggregation-induced emissive(AIE)properties was first found by Tang et al.and caused extensive concern.In 2010,the mechanofluorochromic(MFC)materials with AIE effect were first found by Park,which exploit a new path to synthesis too many MFC compounds.Pyromellitic diimides were a research hotspot of organic fluorescent materials in different fields such as solar cells,electrochemistry,chemical sensors,etc.Pyromellitic diimides were also disturbed by the same ACQ effect as traditional fluorescent materials.Therefore,it is of great significance to design the materials with AIE properties of pyromellitic diimides skeleton.For this study,a series of fluorescent materials with tunable AIE and MFC properties based on pyromellitic diimide unit were designed and synthesized,and their AIE and MFC properties were studied.The main contents are as follows:We used pyromellitic diimide(PMDI)as a skeleton,with indole unit and carbazole units coupling,the synthesis of a series of PMDI fluorescent material,PMDI-In,PMDI-PSCz and PMDI-DSCz.After a series of studies shown that these three compounds were showing an AIE characteristics significantly,enlarged the sizes of the substituent groups with the twisted molecular conformations,the fluorescence emits in aggregate states shown the transition from yellow to red,and molecular has large stokes displacement.At the same time,Gaussian calculation were carried out,shown that the PMDI-In show the plane space structure,proved the mechanical cause of PMDI color can be adjusted by replacing groups conjugated degrees,shown that the color changes after grinding,suggested PMDI-PSCz and PMDI-DSCz is a reversible machinery to change color fluorescent material.These high contrast color changes indicated that the prospect in the application of organic light-emitting materials.We designed and synthesized three kinds of PMDI fluorescent materials with different heteroatomic dense rings according to the AIE properties of indole and carbazole units in the second chapter.Through the studied of the nature of an AIE,we found that when impurity atoms for O,S,N,three kinds of PMDI compounds shown different an AIE phenomenon,PMDI-O in DMF/water solution as the components increase gradually,reached the maximum at 50% when the intensity of fluorescence,fluorescence quenching after increase when water composition,showing obvious phenomenon of ACQ,and PMDI-S and PMDI-N exhibited obvious an AIE phenomenon,and showed a high contrast fluorescence color changed.At the same time,the three compounds were studied mechanically.It was found that PMDI-O had no mechanically chromic properties,while PMDI-S and PMDI-N had good mechanically chromic properties,indicating that heteroatom O could inhibit AIE and mechanically chromic properties of pyromellitic diimide molecules.We designed PMDI fluorescent material based on fluorene unit.After studying its AIE properties,it was found that both PMDI-Ph and PMDI-FL had obvious AIE properties,and their fluorescence intensity showed red shift with the increase of water ratio.