Structure And Properties Of Blue Thermally-activate Delayed Fluorescence Materals Based On Diphenylsulfone

Thermally activated delayed fluorescence(TADF)materials can achieve 100%internal quantum yield(IQE)by converting triplet excitons to singlet excitons through reverse intersystem corssing.These highly efficient,low-cost materials have been widely used in organic light-emitting diodes(OLEDs)which could achieve comparable electroluminescence performance as phosphorescent OLEDs.Among them,satisfying red and green TADF materials have been reported,but blue TADF materials with high efficiency are still rare.On the other hand,due to the close relationship between the photophysical properties of organic solids and the packing patterns of the molecules,the control of the triplet exciton utilization of TADF molecules in different aggregated states needs further study.This thesis focuses on novel blue TADF materials.Push-pull tyged molecules with asymmetrical electro-donors were introduced,and the properties such as molecular band gap,TADF,effect,and proformance of device were investigated through isomer engineering.MP-SOAD and OP-SOAD were designed and synthesized using diphenylsulfone(DPS)as the electron acceptor and 9,9'-dimethylacridine as the electron donor,linking at the 3,4'-,and 2,4'-positions of DPS,respectively.The crystals showed blue emission peaking at 490 and 502 nm,with a fluorescence quantum yield of 33.6 and 49.4%,respectively.They exhibited aggregation-induced fluorescence enhancement and an ultra-small single-triplet energy split of 0.04(MP-SOAD)and 0.09 eV(OP-SOAD),respectively.The devices were fabricated based on MP-SOAD and OP-SOAD as the light-emitting layer,respectively.The MP-SOAD-based device with a doping concentration of 55 wt%achieved the best performance.The maximum brightness,current efficiency,voltage efficiency,and EQE of the device were 3413 cd m-2,32.0 cd A-1,33.5 lm W-1 and 14.7%,respectively.The tert-butyloxy group with smaller steric hindrance and weaker electron-donating ability than 9,9'-dimethylacridine were introduced as the second electron donor,and 2-tert-butyloxy-4'-(9,9'-dimethylacridine)diphenyl sulfone(tBuO-SOpAD)and 2-tert-butyloxy-3'-(9,9'-di Methylacridine)diphenyl sulfone(tBuO-SOmAD)were designed and synthesised.The crystals showed blue emission peaking at 445 and 432 nm,respectively.They exhibited aggregation-induced fluorescence enhancement and an ultra-small single-triplet energy split of 0.02(tBuO-SOpAD)and 0.07 eV(tBuO-SOmAD),respectively.The devices based on tBuO-SOmAD as the light-emitting layer demonstrated,a Lmax,CEmax,PEmax,and EQE of 373 cd m-2,9.28 cd A-1,8.0 lm W-1,and 4.97%,respectively.Weak electron-withdrawing fluoride group was introduced as the second electron acceptor,and 3-fluoro-4'-(9,9'-dimethylacridine)diphenyl sulfone(mF-SOpAD)was designed and synthesized.The crystal showed emission peaking at 461 nm.They exhibited aggregation-induced fluorescence enhancement and an ultra-small single-triplet energy split of 0.04 eV(tBuO-SOmAD),respectively.The nodoped device using mF-SOpAD as the light-emitting layer exhibited a Lmax,CEmax,PEmax,and EQE of 147 cd m-2 and 4.95 cd A-1,1.84 lm W-1,and 2.56%,respectively.