Design And Synthesis Of Advanced Thermally Activated Delayed Fluorescence Emitters With High Efficiency And Their Applications On Oganic Light-emitting Diodes

This thesis mainly focus on developing novel thermally activated delayed fluorescence(TADF)emitters for highly efficient organic light-emitting diodes(OLEDs),and some breakthroughs have been made as listed below:(1)Solution-processed organic light-emitting diodes(OLEDs)have attracted enormous attention owing to their simple manufacture as well as cost-effective.Herein,a novel emitter with thermally activated delayed fluorescence(TADF)feature,named 1,2,3,4-tetrakis(3,6-di-tert-butyl-9H-carbazol-9-yl)thianthrene 5,5,10,10-tetraoxide(4t-BuCzTTR),was developed for solution-processed red OLEDs.Ascribed to the appropriate electron-withdrawing and electron-donating segments as well as large steric effect between the adjacent tert-butyl carbazole moieties,4t-BuCzTTR realizes red fluorescence,significant TADF characteristic,excellent thermal stability and good solution processability.Further utilizing 4t-BuCzTTR as the emitter,the corresponding doped solution-processed OLED with optimal configuration realizes an orange-red emission with a peak at 592 nm and a high maximum external quantum efficiency of 6.2%,which is among the best results of the solution-processed red OLEDs based on pure organic emitters.(2)To obtain highly efficient TADF emitters with high color purity,two novel thermally activated delayed fluorescence(TADF)emitters featuring effective superimposed resonance effect between electron-deficient carbonyls and electron-rich nitrogen atom,were designed and synthesized by utilizing rigid quinolino[3,2,1-de]acridine-5,9-dione(QAD)as the molecular framework,similar with the nitrogen(N)and boron-aromatic(B)systems,3-phenylquinolino[3,2,1-de]acridine-5,9-dione(3-PhQAD)and 7-phenylquinolino[3,2,1-de]acridine-5,9-dione(7-PhQAD)realize significant TADF characteristics with small ?ESTS of 0.18 and 0.19 eV respectively.Moreover,owing rigid molecular framework of QAD,molecular relaxations are dramatically suppressed which favor the requirments of color-purity.In the devices,a maximum EQE of 19.1%(18.7%)as well as a narrow full-width at half-maximum(FWHM)of 44 nm(34 nm)are realized for 3-PhQAD(7-PhQAD).All these superior results reveal that apart from the B/N systems,QAD framework can also act as a TADF matrix with effective resonance effect,and QAD derivatives are ideal candidates to develop TADF emitters with narrow FWHMs for practical applications.