Design, Synthesis And Performance Study Of Orange-red Photothermal Activated Delayed Fluorescent Materials Based On Heterocyclic Compounds

Organic light-emitting diodes(OLEDs)have advantages of high brightness,low power consumption,wide viewing angle,quick response,active luminescence and full color display.They are widely applied in the field of solid state lighting and panel display,with the broad prospects in academia and industry.Under the efforts of domestic and overseas scientists and engineers,the organic electroluminescent materials of third generation have been developed after the traditional fluorescent and phosphorescent materials in recent years.They are also known as thermal activated delayed fluorescence materials,which have the luminescence characteristics of fluorescent and phosphorescent materials.The TADF material is usually used as the guest material of OLED,it is doped with the host material by a certain proportion and the doped material is used as the emitting layer of OLED.Consequently,the rare precious metals such as Iridium(Ir)and Platinum(Pt),required by phosphorescent materials could be avoided and the performance of the device could also be increased.Therefore,the development of new TADF guest materials is particularly important.In this paper,a serious of D-A and D-A-D type pure organic small molecule TADF materials have been designed and synthesized by changing the type and number of substituents of N-phenyl-4-bromo-1,8-naphthalamide,7,10-dibromo-2,3-dicyanopyrazinophen and 2,3,4,5,6-pentafluorobenzonitrile.Simultaneously,the chemical structure,thermal,photophysical,electrochemical and device properties of these materials have been characterized.In Chapter 1,the history,working principle,device structures,performance factors and material classification are briefly introduced.Then the history,fundamental and material type of TADF materials are focused.Finally,the research ideas of this thesis are illustrated.In Chapter 2,synthesized three new compounds of PXZ-NPA,PTZ-NPA and mCP-NPA,through Suzuki and Stille coupling reactions between the groups of phenoxazine,phenothiazine and mCP and the naphthalimide group.These three compounds have excellent thermal stability.The peak fluorescence emission wavelength of PXZ-NPA is 635 nm,which makes it possible to be used as red TADF material.Calculated the energy levels by cyclic voltammetry curves.It is found that they all have deeper LUMO energy levels,shallow HOMO energy levels and smaller energy gaps.These features faciliate the hole and electron transport.The TADF device based on PXZ-NPA as dopant and CBP as host has the best performance.The maximum external quantum efficiency(EQEmax)is 5.1%and the turn-on voltage is 4.0 V.The required voltage is 18.2 V when the brightness reaches 4072 cd/m.In Chapter 3,the guest materials PXZ-DCPP,PTZ-DCPP,DDPhCzDCPP and DDTPACzDCPP were synthesized by simple coupling reaction,based on phenoxazine,phenothiazine,carbazole derivatives and pyrazinophene.It was found that their thermal stability is good with the decomposition temperature as high as 300 ?.The photophysical properties of DDPhCzDCPP and DDTPACzDCPP indicate that they can be used as orange to red TADF materials.The energy gap of PXZ-DCPP is the smallest,which is only 1.26 eV.The TADF device containing PXZ-DCPP exhibits the best performance.The EQEmax can reach 17.4%and the turn-on voltage is 3.2 V.When the brightness reaches 11766 cd/m2,the driving voltage is 15.2 V.In Chapter 4,the four target products of 3PXZFCN,4PXFCN,3PTZFCN and 4PTZFCN were prepared with phenothiazine and phenoxazine,respectively.The electrochemical,thermal and photophysical properties of the four compounds were studied.The thermal stability of 3PTZFCN is the best with the decomposition temperature reaching 405 ? and the glass transition temperature reaching 130 ?.The study of photophysical properties suggests that 4PXZFCN can be used as the orange light material.The EQE values of devices based on 3PXZFCN,4PXFCN,3PTZFCN and 4PTZFCN are 2.3%,3.3%,1.7%and 2.1%,respectively.The device using 4PXZFCN shows the best performance.The turn-on voltage is 3.8 V,and the driving voltage is 13.6 V when the brightness reaches 5158 cd/m2.In Chapter 5,the research contents of this thesis are summarized and the development of TADF OLEDs is forecasted.