Synthesis And Properties Of AIE And AIE-TADF Materials Containing Phenylethene Units

In recent years,organic light emitting diode（OLED）has become a hot research field in both academia and commercial circles,due to its potential applications in solid state lighting and flat panel displays.In OLED devices,it generally emploies carrier transport and multilayer structures of light-emitting layers（EMLs）to efficiently harvest electron excitons and thus emit light.Therefore,the performance of fluorescent material affects the fabrication of efficient and stable OLED devices.The phenomenon of aggregation-induced emission（AIE）first found by Tang’s group,has solved the problem of aggregation caused quenching（ACQ）which has restricted the development of traditional fluorescent materials.The discovery of AIE provides a way to obtain fluorescent materials with high solid luminescence efficiency.On the other hand,thermally activated delayed fluorescence（TADF）materials has become a hot topic in recent years due to that they can harvest both singlet and triplet excitons to achieve an internal quantum efficiency of nearly 100%.Based on the character of AIE materials,AIE molecules with TADF characteristics（AIE-TADF）are thought as a promising strategy to solve the problem of a maximum IQE are limited to be 25%for AIE materials.Some researchers have tried to combine the groups with AIE characteristics and units with TADF characteristics,and the obtained compound is likely to be endowed with AIE and TADF properties.This material,term AIE-TADF,avoids the limit of internal quantum efficiency of AIE materials up to 25%,and avoids the ACQ effect of TADF materials.It is a new kind of luminescent material which is more suitable for OLED.Among the currently reported AIE molecules and TADF molecules,triphenylethylene（TrPE）/tetraphenylethylene（TPE）is a common AIE active molecule,and it has the character of ease of synthesis and modification;Carzole is a rich electron group and possesses good hole-transporting property;thianthrene-9,9,10,10-tetraoxide has a suitable LUMO energy level（2.90 eV）,and it is often used as TADF unit.Based on the analysis above,we have designed and synthesized two kinds of fluorescent materials with AIE characteristics including TrPE/TPE and dicarbazole,and two AIE-TADF materialscontainingTrPE/TPE,carbazoleand thianthrene-9,9,10,10-tetraoxide.Their photophysical properties,thermal stability and electroluminescent properties have been systematically investigated.The main contents are as follows:In chapter 1:Through literature research,the development process,luminescent mechanism and kinds of organic electroluminescent device,aggregation-induced emission materials,thermal activation delayed fluorescence materials,AIE-TADF materials possessing AIE and TADF properties are reviewed.In chapter 2:Two fluorescent materials with AIE characteristics,PPBC and DPPBC,are designed and synthesized by fusing TrPE/TPE and dicarbazole.The photophysical properties,thermal stability and electrochemical properties of these two compounds are systematically investigated and analyzed.The electroluminescent properties of these two compounds applied to OLED are also discussed in this chapter.The results show that electroluminescent devices constructed with DPPBC as light-emitting layer have better electroluminescent properties,and their maximum brightness and maximum current efficiency are 10290 cd m^-2 and 4.075 cd A^-1,respectively.In chapter 3:Two AIE-TADF compounds ECPPTT and ECDPTT are obtained by integrating tetraphenyl/triphenyl-ethene（TPE/TrPE）,carbazole group and thianthrene-9,9,10,10-tetraoxide unit.Their photophysical properties and delayed fluorescence properties are systematically investigated.Theoretical calculations are used to investigate the orbital overlap of the two molecules.And we have also studied their thermal stability and electrochemical stability.Finally,non-doped OLED are prepared using these two compounds as luminescent layer,their electroluminescent properties are analyzed.The results show that the OLED prepared by ECPPTT,has better electroluminescent properties,performing the maximum luminance and current efficiency of 10090 cd m^-2,3.347 cd A^-1.