Novel AIE-TADF Materials: Synthesis,property And Application

Organic luminescent materials are an important part of organic semiconductor materials,owing to their great potential in organic optoelectronic devices,chemosensors,biosenors,etc.However,most organic luminescent materials encounter severe concentration or aggregation-caused quenching(ACQ)problem,which limits their practical applications.The ACQ problem also troubles the thermally activated delayed fluorescence(TADF)materials,which are regarded as the third generation organic luminescent emitting materials.Fortunately,aggregation-induced emission(AIE)fistly reported in 2001 is hopefully able to solve the ACQ problem.Therefore,developing AIE-TADF molecules can promote the industrialization of the organic luminescent materials.Under the guidance of AIE mechanism and donor-acceptor(D-A)design concept for TADF materials,the studies in this thesis are the development of AIE-TADF molecules and exploration of their applications in organic light-emitting diodes(OLEDs)and time-resolved fluorescence imaging.In chapter 2,by adopting phenoxazine or phenothiazine as the D and diphenylsulphone or dibenzothiophene-S,S-dioxide as the A,we designed a series of AIE-TADF molecules with D-A framework,namely,DPS-PXZ,DBTO-PXZ,DPS-PTZ and DBTO-PTZ.By the measurment of the optical spectra and fluorescence quantum yields,we discussed the photophysical properties of the four molecules and then studied the main cause for their AIE and TADF properties,assisted by theory calculations.So far,the reported AIE-TADF molecules are mostly applied in OLEDs,and seldom used in bioimaging.In chapter 3,we adopted carbonyl as the A and phenoxazine or phenothiazine as the D,and then synthsized a series of AIE-TADF molecules,namely,BP-2PXZ,BP-2PTZ,BP-PXZ and BP-PTZ.We encapsulated those four molecules within bovine serum albumin to generate fluorescent nanoparticles and then applied those fluorescent nanoparticles in time-resolved fluorescence imaging based on the long fluorescence lifetime of the TADF.The results showed that those fluorescent nanoparticles had low cytotoxicity and good application to time-resolved cell imaging.In chapter 4,by adopting cyano as A and carbazole or 3-bromocarbazole as D,we synthsized a series of D-A molecules exhibiting both AIE and mechanoluminescence,namely,CzFPN,Br CzFPN and 2CzPN.Combining with the crsystal data,we gave some explanations about the casue of the mechanoluminescence.It was demonstrated that piezoelectric space group,noncentrosymmtric molecular arrangement and high solid-state fluorescence were the cause for the mechanoluminescence.In chapter 5,we introduced Br atom into the TADF molecules to improve the TADF property,and thus promote the performance of the OLEDs.We designed AIE-TADF molecules with two(2BrCzPN),one(BrCzCzPN)or no Br(2CzPN)atoms,and then fabricated three OLEDs based on them.The results showed that the performance of the OLED based on 2BrCzPN containing two Br atoms is the best and that of based on 2CzPN containing no Br atom is the worst among the three OLEDs.The OLED based on 2BrCzPN provided maximum current efficiency and external quantum efficiency of 31.5 cd A-1 and 12.3%,respectively.