Tetraphenylbenzene-based Aggregation-induced Emission Luminogens: Synthesis And Optoelectronics Application

Organic luminescent materials are promising candidates as light-emitting diodes,bioimaging probe,sensors and memory devices.The fabrication of novel luminous compounds with simple molecular structure,facile tunability and thermal stability is desirable to construct excellent molecular devices.Most of the luminescent materials often suffer from aggregation-caused quenching(ACQ)effect,where they emit bright emission at dilute solution while exhibit weak or even no emission in aggregate state.In contrast,aggregation-induced emission(AIE)luminogens(AIEgens)are weak or non-emissive in dilute solution because their excited states undergo non-radiative decay via intermolecular motions whereas exhibiting intense luminescence in solid state.AIE can solve the ACQ problem,and hold great technological value for practical applications.The past 20 years have witnessed the rapid development of AIE research,from restriction of intramolecular rotations to restriction of intramolecular motions,from aggregation-induced emission to aggregate science,and many original results have been achieved.However,there are still some challenges.For example,multi-functional AIEgens need to be further developed;deep blue AIEgens with high efficiency and pure color are rare because the presence of heteroatoms or double bonds in many AIEgens generally lead to red-shift of their emission.Therefore,the applications of AIEgens in non-doped deep blue organic light-emitting diodes(OLED)still have a huge room for development.Delightfully,tetraphenylbenzene(TPB),a new AIEgen with a solid emission peak at 363 nm,which is much suitable for the construction of deep-blue emitter.Benefiting from its high emission efficiency in the film state,the non-doped deep blue device based on TPB-based AIEgen realizes excellent device performance.However,the design strategy for the construction of AIEgens applicable in fabrication of non-doped deep blue OLEDs with high performance is scare In addition,the CIEy value is still larger than 0.08.Based on this research background,the research content of this thesis is as follows:In Chapter 2,novel TPB based deep blue AIEgens with various donor units and an acceptor of cyano(CN)group are developed and used to fabricate non-doped deep blue and hybrid white OLEDs.Thanks to the high emission efficiency,the high proportion of horizontally oriented dipoles(83.6%)in the film state,balanced hole and electron transporting capacity of TPB-PAC,and the process of T₃?S₁ transition,a deep blue device with excellent external quantum efficiency(EQE)of 7.27%(CIE=0.15,0.08)and low efficiency roll-off was achieved by using it as emitting layer(EML).Moreover,efficient two-color hybrid warm white OLEDs(CIE=0.43,0.45)were achieved using TPB-PAC as the blue-emitting layer and phosphor doped host,which realized maximum EQE of 19.1%.This work provides a general strategy to achieve high performance,stable deep blue and hybrid white OLEDs by construction of AIEgens with excellent horizontal orientation.In Chapter 3,we further designed and synthesized a new type of violet-blue AIEgens by replacing the triphenylamine(TPA)group with carbazole derivatives with weaker electron donating ability.Benefiting from its absolute photoluminescence quantum yield(?_PL)higher than 98%in their film states,the TPBCz C1-based non-doped OLED exhibits a high EQE of4.34%with CIE coordinates of(0.160,0.035),which represents the first example of non-doped violet-blue AIEgen-based OLED with CIEy smaller than 0.046.Meanwhile,the TPBCz C2-based OLED also achieved a maximum EQE of 4.78%and CIE coordinates of(0.159,0.060).This work provides a practical molecular design strategy for violet-blue emitters,which is crucial for next generation ultra-high definition television(UHDTV)display standard.In Chapter 4,we further studied the influence of the substituents of the longitudinal axis of TPB on luminescence properties of AIEgens.The bright emission in both dilute solution(e.g.,?_PL=90.2%in THF)and aggregate state(e.g.,?_PL=92.7%in film,?_PL=95.3%in crystal)were achieved by combining planar and distorted structures with charge transfer effect.Benefiting from their excellent thermal stabilities,the non-doped deep blue device based on2Me2PB-AC realized a maximum EQE up to 4.75%with CIE coordinates of(0.15,0.05).These compounds are also demonstrated as promising guest embedded into crystalline host matrix to achieve efficient room temperature phosphorescence and apply for the information encryption.In Chapter 5,novel TPB based blue isomers with double donors of TPA and acceptors of CN groups were developed and used to fabricate non-doped blue OLEDs.The influence of the intermolecular interaction on the luminescence of AIEgens were deeply explored.Benefiting from its high emission efficiency in the film state,the non-doped blue device based on i TPB-2AC realized a maximum EQE of 8.21%,which is one of the best results for non-doped blue OLEDs based on AIEgens.Meanwhile,the TPB-2AC-based OLED also achieves a maximum EQE of 5.92%.More importantly,the EQE value could also remain 5.71%at the luminance of1000 cd m^-2,demonstrative of a very low roll-off.The emission properties of the AIEgens in aggregate state could be control by changing the position of the donor and acceptor groups.This work provides a practical molecular design strategy for the construction of non-doped blue OLEDs.In Chapter 6,novel blue AIEgen of TPA-An-m Ph CZ was designed and synthesized.TPA-An-m Ph Cz show excellent thermal stability and high PLQYs in their film state.The non-doped device exhibits excellent device performance.The maximum EQE of TPA-An-m Ph Cz-based OLED can reach up to 8.10%,respectively,with an operation voltage as low as 3.0 V.More importantly,the EQE still remain a high value of 6.97%,respectively,at a luminance of 1000cd m^-2,suggesting low efficiency roll-off of the device.The transient EL spectra and theoretical calculation confirm that the unique triplet-triplet upconversion process of the emitter plays a crucial role in high EQE.The design idea for the novel triplet-triplet upconversion and aggregation-induced emission is valuable for the construction of high-performance OLEDs,which may be beneficial for practical applications,such as white lighting and full color flat-panel displays.