Design,Synthesis And Application Of Multifunctional Aggregation-Induced Delayed Fluorescent Materials

As a new type of organic light-emitting material,aggregate-induced delayed fluorescence?AIDF?materials,have excellent photoluminescence efficiency and prominent delayed components in the solid state.These materials combine the advantages of aggregation-induced emission?AIE?and delayed fluorescence,which can efficiently suppress concentration quenching and exciton annihilation,and harvest 100%of excitons.Hence,AIDF materials are of great significance for the preparation of electroluminescent devices with high efficiency and low roll-off.In this thesis,a series of multifunctional AIDF materials were designed and synthesized.They not only exhibited excellent photoluminescence efficiency and delayed fluorescence in the aggregated state,but also showed through-space charge transfer or mechanochromic luminescence?MCL?property.Through systematic investigation,we eluciated the structure-property relationship of these materials and explored their applications in organic light-emitting diodes?OLEDs?.In Chapter 2,two tailor-made luminogens TRZ-HPB-PXZ and TRZ-HPB-DMAC,comprising of electron donors?phenoxazine and 9,9-dimethyl-acridine?and acceptor?triazine?bridged by the through-space conjugated hexaphenylbenzene?HPB?were synthesized and characterized.The crystal and electronic structures revealed that the peripheral phenyls in HPB were closely aligned in a propeller-like fashion,rendering efficient through-space charge transfer between donor and acceptor moieties.These molecules displayed weak fluorescence with negligible delayed component in solutions but strong fluorescence with greatly increased delayed component upon aggregate formation,namely aggregation-induced delayed fluorescence?AIDF?.Their neat films exhibited high photoluminescence quantum yields?PLQY?,and prominent delayed fluorescence.The nondoped OLEDs based on these new luminogens exhibited excellent performance with maximum external quantum efficiency of12.7%and very small efficiency roll-off of 2.7%at 1000 cd m^-2.In Chapter 3,by adopting strong electron-withdrawing tetra-coordinated phenylpyridine boron as acceptor,and phenothiazine or phenoxazine as donor,we obtained a series of multifunctional organic light-emitting materials PPYB-BPTZ,PPYB-PTZ,PPYB-BPXZ and PPYB-PXZ.These materials all displayed obvious AIDF characteristics,and the emission and delayed component of these materials were significantly enhanced in the solid state.Under external stimuli,PPYB-BPTZ and PPYB-PTZ showed obvious MCL phenomenon,and the morphologically dependent emission property could be attributed to the change of molecular conformation.Finally,we studied the electroluminescence properties of these materials,and PPYB-BPXZ-based OLEDs achieved the best efficiency.In Chapter 4,by adopting tetra-coordinated phenylpyridine boron as acceptor,and acridine derivatives as donor,we designed and synthesized a series of multifunctional organic light-emitting materials PPYB-DMAC,PPYB-SPIRO-AC,PPYB-FA and PPYB-DPAC.Photophysical tests demonstrated the AIDF characteristics of the four materials.By controlling the preparation method,we obtained two kinds of crystals of PPYB-DPAC,and different crystalline states could be converted by grinding.In addition,PPYB-DPAC also exhibited polymorph-dependent delayed fluorescence,which was related to the varied conformation of the molecule in different aggregated states.Finally,we used these materials as light-emitting materials to prepare OLEDs,among which PPYB-SPIRO-AC-based OLEDs achieved the best efficiency.