New AIE-Active Luminescent Materials And Host Materials:Synthesis And Applications In Organic Light Emitting Diodes

So far,aggregation-induced emission?AIE?has become a hot research topic in the field of materials and chemistry.In order to perfect the theoretical system of AIE,mechanism exploration,system expansion and application development of AIE compounds have become the main research directions.Organic luminescent materials with AIE properties are ideal emitters for preparing high-efficiency organic light emitting diodes?OLEDs?,because of the advantages of high luminescence efficiency and weak intermolecular interaction in the solid state.In this thesis,a series of new AIE compounds were designed and synthesized.We discussed the structure-activity relationships and developed novel functions of these organic luminescent materials.Moreover,highly efficient OLEDs with greatly improved efficiency statbility had been fabricated with these new AIE compounds.In chapter 2,a series of asymmetric D-A-D'molecules,CP-BZ-PPXZ,CP-BZ-MPPXZ,CP-BZ-PDMAC and CP-BZ-MPDMAC,were designed using 9-phenyl-9H-carbazole,phenoxazine and 9,9-dimethyl-9,10-dihydroacridine as electron-donating groups and carbonyl groups as electron-withdrawing groups.By adjusting the conjugation length and steric hindrance of these four molecules,we discussed the photophysical properties and structure-activity relationship.Using the four molecules that possessed excellent photophysical properties,we had prepared highly efficient OLEDs.The external quantum efficiency and current efficiency of nondoped devices using PC-BZ-PPXZ as emitting layers were as high as 11.8%and 30.90 cd A^-1,respectively.And the efficiency roll-off of these devices was low.In chapter 3,we designed and synthesized two gold?I?complexes C₆F₅Au-Py-PPXZ and C₆F₅Au-Py-PDMAC using pyridine as ligand and pentafluorobenzene,phenoxazine and9,9-dimethyl-9,10-dihydroacridine as unique function groups.Different from traditional transition metal complexes,C₆F₅Au-Py-PPXZ and C₆F₅Au-Py-PDMAC exhibited AIE property and delayed fluorescence emission,instead of phosphorescence emission.And the fluorescence quantum yields of these two gold?I?complexes in thin films are 23.5%and60.5%,respectively.Solution-processed OLEDs fabricated using these two materials as emitting layers provided excellent device performance.The maximum external quantum efficiency and luminance of doped OLED based on C₆F₅Au-Py-PPXZ were 8.20%and 14 311cd m^-2,respectively.In chapter 4,four bipolar host materials,DPBP-DMAC,DPMBP-DMAC,DPBP-CZ and DPMBP-CZ with AIE characteristics,were designed and synthesized using carbazole and9,9-dimethyl-9,10-dihydroacridine as hole-transporting groups,and pyridine as electron-transporting group.These four hosts were employed to fabricate a series of monochromatic OLEDs with different phosphorescent dopants,including blue emissive FIrpic,green emissive Ir?ppy?₂?acac?,and red emissive Ir?piq?₂?acac?.The results indicated that these four materials could be universal bipolar host materials for phosphorescent OLEDs.The external quantum efficiences of blue,green and red OLEDs using DPMBP-DMAC as the host were as high as 25.12%,24.73%and 19.71%.More importantly,the efficiency roll-off of all the devices was very small,demonstrating the greatly imporved efficiency stability of the phosphorescent OLEDs based on these new host materials.