Design,Synthesis And Photoelectric Property Investigation Of Organic Functional Materials With TADF And AIE Features

Organic light-emitting diodes（OLEDs）have great development prospect and application potential in solid state lighting and panel display due to low power consumption,quick response speed,high resolution and light flexible display.OLEDs have been the focus of research and commercialization for nearly two decades.Luminescent materials are the key factor of the influence for OLEDs performance.Compared with conventional fluorescent materials with 25%exciton utilization and phosphorescent materials with metal-organic framework,thermally induced delayed fluorescence（TADF）materials can efficiently utilize singlet（S₁）and triplet（T₁）excitons through reverse intersystem crossing（RISC）.Moreover,the use of pure organic structure without precious metals endows TADF materials with low cost,structural diversity and easy modulation of emission wavelength,which has gained widespread attention.However,in order to decrease the excition quenching from high excition density,TADF materials usually employed the host-guest system which will increase the risk of phase separation and complexity.Aggregation-induced emission（AIE）luminogens process the features that the PL intensity is weak in dilute solutions while becomes stronger in aggregated state;therefore the notorious concentration quenching in aggregated state can be inhibited.Hence,developing novel AIE-active TADF materials which can achieve 100%IQE and alleviate the harmful concentration quenching simultaneously,is potential for nondoped OLEDs.The main work of this paper is to develop fluorescent materials with AIE and TADF features bearing triphenylamine（TPA）,carbazole（Cz）,9,9-diphenyl-9,10-dihydroacridine（DPAC）,9,9-dimethyl-9,10-dihydroacridine（DMAC）,and phenoxazine（PXZ）as donors,benzophenone（BP）and derivatives as acceptors.The concrete research is as follows:1.A series of AIE-active TADF emitters,bearing TPA as donor and phenyl ketone as acceptor unit,were developed.The influence of charge transfer categories（through-bond（TBCT）and through-space（TSCT））on luminescent properties is investigated respectively by controlling the relative position of the donor and acceptor.When the charge transfer category is through-space,the RISC rate progressively improved by virtue of the narrower energy split between singlet and triplet states(（35）E_ST),meanwhile,the restricted intramolecular motion suppresses the nonradiative decay effectively,resulting in obviouslly improved luminescence efficiency.Solution-processed OLEDs based on TSCT emitter（4-（9H-carbazol-9-yl）phenyl）（4-（1-（4-（diphenylamino）phenyl）-9H-carbazol-9-yl）phenyl）methanone（1TCPM-Cz）)achieve maximum current efficiency（CE）of 35.5 cd A^-1 and external quantum efficiency（EQE）of13.3%,respectively.2.Two novel emitters exhibiting TADF and AIE features were developed,named as（4,4’’-bis（diphenylamino）-[1,1’:4’,1’’-terphenyl]-2’-yl）（dibenzo[b,d]thiophen-2-yl）methanone（DTPA-DTM）and（4,4’’-bis（diphenylamino）-[1,1’:4’,1’’-terphenyl]-2’,5’-diyl）bis（dibenzo[b,d]thiophen-2-ylmethanone）（DTPA-DDTM）,where charge was transferred through the covalent bond and through space.Benefiting from the twisted structure and enhanced degree of CT interactions through introducing dual functional acceptors,the PLQYs of DTPA-DDTM in solid state improved obviously compared with DTPA-DTM.By combining charge transfer pathways,small（35）E_ST（0.17 e V）and high radiative efficiency（60.5%）were achieved.Through effectively suppressing the exciton quenching,nondoped OLEDs employing DTPA-DDTM achieved the maximum CE and EQE of 25.6 cd A^-1 and 8.2%,respectively.3.A class of emitters exhibiting TADF and AIE featuress,which containing phenyl（pyridyl）methanone cores as acceptor and di（tert-butyl）carbazole and DMAC（or PXZ）as donors,were developed.By adjusting the position of N atom in the acceptor group,the intramolecular hydrogen bonds could be constructed at different positions in the molecule.The presence of intramolecular hydrogen-bonding was confirmed by crystal structure and theoretical simulation and the physical properties,thermal stability,solution process,device performance were investigated systematically.With the intramolecular hydrogen-bonding interactions,reduced（35）E_ST,suppressed non-radiative decay and increased the luminescence efficiency could be achieved in the emitters concurrently.Solution-processed nondoped OLEDs adopted（6-（3,6-di-tert-butyl-9H-carbazol-9-yl）pyridin-3-yl）（4-（9,9-dimethylacridin-10（9H）-yl）phenyl）methanone（3CPy M-DMAC）as emitter exhibiting a maximum CE and EQE of 35.4 cd A^-1 and 11.4%,respectively.4.A serious of AIE-active TADF emitters adopting phenyl ketone as acceptor group and DPAC（or DMAC and PXZ）as donor unit were designed and synthesized.By matching electron-accepting segment phenyl ketone with various electron-donating units including DPAC,DMAC and PXZ moieties,the emission color could be tuned from blue to green-yellow.The comparative study of TADF and AIE characteristics was established between the dendrimers and reference non-dendritic luminogens through physical properties,thermal stability,film-forming ability and device performance.By employing the tortile TPA units as molecular central core and introducing circumambient donor-acceptor arms with nearly orthogonal configuration,the highly twisted molecular structure was realized.Therefore,the improved PLQYs and more efficient RISC process were realized simultaneously resulted from the suppressed intermolecular interaction and stacking in aggregated state of these dendrimers.Consequently,Solution-processed nondoped and doped device with maximum EQEs of 12.1%and 17.6%were achieved when employing the dendritic luminogens of（（nitrilotris（benzene-4,1-diyl））tris（6-（2-ethylhexyl）-9H-carbazole-9,3-diyl））tris（（4-（10H-phenoxazin-10-yl）phenyl）methanone）（3PXZ-BPCTPA）as emitter.