Synthesis And Properties Of New D-π-A Conjugated Small Molecules And Polymers Containing 2,6-diphenyl-4-arylpyridine Structure

In recent years,conjugated organic molecules with donor acceptor structures have attracted extensive attention in solar cells,OLEDs,sensors and other fields.Therefore,the design and synthesis of luminescent molecules with good luminescence performance,strong stability and easy regulation are the focus of current research.Since the discovery of conductive polymers,the photoelectric properties of conjugated polymers have attracted extensive attention from researchers.Tetraphenylethylene,carbazole and fluorene are all electron-rich donor units,which have strong electron-giving ability and good hole transport.When they are introduced into the polymer structure and combine with the acceptor unit to form D-π-A type conjugated polymer,due to the molecular hybridization between the acceptor and donor,These polymers are prone to intramolecular charge transfer（ICT）in the low energy region of the spectrum.Therefore,D-π-A conjugated polymer has good optoelectronic properties and all the mechanical properties of polymer materials.On the basis of comprehensive literature,several new luminescent molecules with 2,4,6-triarylpyridine as parent structure were designed and prepared in this paper.Meanwhile,the synthesis and properties of D-π-A conjugated polymers containing2,4,6-triarylpyridine structure were studied.The main work includes the following three parts:1.Using 4-bromoacetophenone,aromatic benzaldehyde and ammonium acetate as raw materials,four 2,6-bis（4-bromophenyl）-4-aryl pyridine derivatives containing methyl,methoxy,trifluoromethyl and without substituents were synthesized by Chizibabin reaction,and then reacted with PdCl₂（PPh₃）₂ and CuI,respectively.Four derivatives of 2,6-bis（4-acetylphenyl）-4-arylpyridine with AIEE were prepared.It was found that the absorption wavelengths and solid-state fluorescence emission wavelengths of the four compounds were affected by introducing groups by optical properties tests.The difference of electron cloud density between the highest occupied orbital（HOMO）and the lowest vacant orbital（LUMO）of these compounds is small.2.On the basis of the above studies,in order to design fluorescent small molecules with better light performance,four new D-π-A tetrastyrene-acetylphenyl-substituted pyridine conjugated small molecules were synthesized by introducing tetraphenylethylene units through Sonogashira coupling.AIE test showed that the series of molecules exhibited obvious aggregation induced luminescence（AIE）phenomenon.At the same time,the series of small molecules showed good photoelectric properties,the highest quantum yield of 83.00%.The electron cloud distribution of HOMO and LUMO levels calculated by density functional theory shows that these molecules have good electron transfer ability.3.In order to investigate the effect of extension of conjugated chain on fluorescence,eight new D-π-A conjugated polymers were synthesized by Sonogashira coupling triarylpyridine containing methyl and trifluoromethyl with electron-rich donators such as tetraphenylethylene,carbazole and fluorene,respectively.These polymers all exhibit good fluorescence emission in solution,which provides a certain possibility for sensing applications.Then the properties of the polymer were studied through a series of performance tests.The preliminary study shows that the series of polymers are amorphous structures.It has excellent thermal stability and the maximum thermal decomposition temperature can reach 481℃.It is soluble in toluene,tetrahydrofuran and other conventional solvents at room temperature.