Synthesis And Characterization Of Fluorescent Host And Thermally-Activated Delayed Fluorescence Materials

White organic light emitting diodes(WOLEDs)as a new type of solid lighting source,have drawn considerable attention due to its high efficiency,low power consumption,light weight,fast response and realizing flexible display.Numerous approaches have been developed to produce WOLEDs.Among them,fluorescent and phosphorescent(F–P)hybrid WOLEDs is considered as the promising approach.However,it is difficult to achieve a blue fluorescent material that not only possesses high effiency,but also has a high triplet energy level enough to sensitize a phosphorescent dopant.Recently,Thermally activated delayed fluorescence(TADF)OLEDs that break the 25 % theoretical quantum efficiency of traditional fluorescent OLEDs,have been widely concerned due to the possibility of achieving 100 % internal quantum efficiency.Compared with traditional phosphorescent OLEDs containing phosphorescent materials doped with heavy metal,TADF OLEDs using fluorescent materials can reduce device cost and increase life-time and spectral stability of devices due to replace phosphorescent materials.The contents are as follows:Firstly,a blue fluorescent small molecule host material,named BFP-PTPA,was synthesized through a phenyl linkage between benzofurylpyridine as the acceptor and triphenylamine as the donor.The structure of BFP-PTPA was verified by 1H NMR and mass spectrometry.Thermal gravimetric analysis result reveals that BFP-PTPA has thermal decomoposition temperature(Td),corresponding to 5 % weight loss at 245 ℃.BFP-PTPA has a high triplet energy level(ET=2.58 eV),calculated from low temperature phosphorescence spectra.The HOMO level of BFP-PTPA was estimated to be-5.47 eV by cyclic voltammetry.Fluorescence/phosphorescence white organic light emitting diodes were fabricated with BFP-PTPA as a host material and PO-01 as a dopant material.Device doped with 0.4 wt.% of PO-01 depicted a maximum luminous efficiency of 6.9 cd/A,a maximum power efficiency of 2.7 lm/W and CIE(0.41,0.45);while doped with 0.8 wt.% of PO-01,device showed a maximum luminous efficiency of 6.8 cd/A,a maximum power efficiency of 1.89 lm/W and CIE(0.43,0.46).Secondly,two blue fluorescent polymer host materials,PSOTPA and PSOCz were synthesized by the molecular structure of D-π-A.The thermal stability of polymers was measured by TGA and DSC.These results reveal that PSOTPA and PSOCz depicted Tds around 241 ℃ and 278 ℃,and glass transition temperatures(Tg)around 104 ℃ and 120 ℃,respectively.The HOMO energy levels of the polymers measured by cyclic voltammetry were estimated to be-5.50 and-5.48 eV.Both of PSOTPA and PSOCz have a ET of 2.40 eV,calculated from low temperature phosphorescence spectra,which was higher than that of the orange dopant,eq.PO-01.This suggested that PSOTPA and PSOCz could be used as host materials to fabricate F/P WOLEDs.Thirdly,a series of TADF materials,PTZ-TROZ,bis-PTZ-TROZ and triPTZ-TROZ was synthesized,composed of heterocyclic triazine as the acceptor and phenothiazine as the donor.The structures of the compounds were verified by 1H NMR and mass spectrometry.The thermal stabilities of the materials were measured by TGA and DSC.These results reveal that Td and Tg were 328 ℃、75 ℃,365 ℃、94 ℃ and 421 ℃、114 ℃.The HOMO energy levels of PTZ-TROZ,bis-PTZ-TROZ and tri-PTZ-TROZ measured by cyclic voltammetry were estimated to be-5.47,-5.45 and-5.43 eV.Fluorescence quantum yields and fluorescence lifetimes of PTZ-TROZ,bis-PTZ-TROZ and tri-PTZ-TROZ were investigated,and these results show three materials could emit delayed fluorescence.