The Studies Of Structure-property Relationship And Electroluminescence Application Based On Aggregation-induced Emission Luminogens

The immense interest in organic light-emitting materials is driven mostly by their tremendous utility in the fields of organic light-emitting diodes?OLEDs?,organic light-emitting transistors,organic lasers,chemosensors and bioprobes,etc.Because these materials are practically used in their condensed phases,such as aggregates or solid films,the performance of optoelectronic devices or sensors heavily depends on the inherent physicochemical properties of molecular aggregates,especially the emitting efficiency in solid state.However,most conventional organic light-emitting materials suffer serious aggregation-caused quenching?ACQ?effect in the aggregate state.This ACQ problem has limited the practical application of organic light-emitting materials to some extent.Aggregation-induced emission?AIE?is currently recognized as the most effective way to overcome ACQ problem.AIE concept firstly proposed by Professor Ben Zhong Tang in 2001has developed into a frontier research in the field of chemistry and materials science nowadays and researchers worldwide have enthusiastically engaged in AIE study.Even so,there are still some basic scientific problems and challenges in AIE field,such as the AIE mechanism needs to be further confirmed and understood;excellent multi-functional or blue AIE materials still need to be developed;the performance of OLEDs based on AIE materials urgently needs a breakthrough.Opportunities and challenges coexist.To this end,the research content of this thesis is as follows:In Chapter 2,a series of silole derivatives substituted with benzo[b]thiophene?BT?at the 2,5-positions of the silole ring were synthesized and fully characterized.Great efforts were devoted to figure out the impacts of connection manners between BT and silole rings on the photophysical properties of the resulted molecules.Theoretical calculations disclose that the good conjugation restricts the intramolecular rotational motions and blocks the nonradiative channels,which enables the molecules to emit more efficiently in solutions.But the well-conjugated planar backbone is prone to form strong intermoelcular interactions in the aggregated state,which decreases the emission efficiency.These results not only provide more evidences to support the RIR?restriction of intramolecular rotations?mechanism but also offer deep insight into structure-property relationship of silole derivatives,which are conducive for the further design of silole-based functional materials.In Chapter 3,Tetraphenylfuran?TPF?and its control molecule of tetraphenylthiophene?TPT?were synthesized.Surprisingly,its photo-physical property investigation showed that TPF shows the aggregation-caused quenching effect instead of AIE characteristic,whereas,TPT exhibits quite weak AIE effect.Combining the experimental results and theoretical calculation as well as the conclusion of Chapter 2,this phenomenon was concluded to co-cause by the RIR and conjugation effect.Thus,this work provides an insight understanding of RIR,which will great promote the development of AIE.In Chapter 4,a series of n-type AIE materials comprised of 2,3,4,5-tetraphenylsilole and benzimidazole or phenanthrylimidazole functional groups were wisely designed and synthesized.They possess high solid-state emission efficiency,good thermostability and low LUMO level.Surprisingly,their electron mobility could reach up to 10^?4 cm² V^?1 s^?1 order.As a result,they perform excellently in non-doped OLEDs.For instance,their"standard"three-layer OLEDs can achieve the high EL efficiencies of 15.06 cd A^?1,16.24 lm W^?1 and4.84%.And their double-layer devices in which the siloles were adopted as both light emitter and electron transporter afford excellent performances with high EL efficiencies up to 13.30cd A^?1,14.51 lm W^?1 and 4.25%,which is rare for this kind of double-layer device.This work has developed the excellent n-type AIE materials and provides a useful design strategy for n-type solid-state emissive materials and highlights the advantage of AIE materials in simplifying the configuration of OLEDs.In Chapter 5,we designed and prepared a blue AIE emitter?TPE-tAnPBI?based on tetraphenylethylene derivative.TPE-tAnPBI has good thermal stability and high solid-state emission efficiency.By utilizing TPE-tAnPBI as the light-emitting layer,we constructed a series of non-doped OLEDs,whose EL color is close to the deep blue region and EL efficiency is optimized to 7.21 cd A^?1,6.78 lm W^?1 and 5.73%.This performance is the best among the reported non-doped blue OLEDs based on AIE materials.At the same time,we also prepared a doped device based on TPE-tAnPBI,and its EL light blue shift to deep blue region and external quantum efficiency reach up to 5.45%.In Chapter 6,we constructed a series of high-performance doped and non-doped OLED devices based on novel aggregation-induced delayed fluorescence?AIDF?materials.By utilizing CBP as host material and modulating the doping concentration of AIDF guest,we studied the effect of doping concentration of AIDF materials on the performance of their doped OLEDs.We found that with the increase of doping concentration,the driving voltage of OLEDs is decreased,the luminance is advanced and the efficiency roll-off is obviously reduced.Based on these new AIDF materials,we also obtained some highly efficient non-doped OLEDs,in which L_max,?_C,max,?_ext,max,?_P,max are as high as 100290 cd m^?2,59.1cd A^?1,18.4%and 65.7 lm W^?1,and the efficiency roll-off is very small.In the currently reported non-doped OLEDs,the overall performance of this device is almost the most excellent,even can comparable with the doped OLEDs fabricated from the traditional delay fluorescent or phosphorescent materials.Due to unique AIDF attribute and weak intermolecular interactions,these novel light-emitting materials both have excellent solid-state luminescence quantum yields and high exciton utilization,and can alleviate the annihilation process between high concentration excitons in the devices,so the OLEDs can maintain excellent EL performance at high exciton concentration.This work is undoubtedly a breakthrough for the application of AIE materials in OLED devices and provides an effective strategy for the construction of non-doped OLEDs with high efficiency,low roll-off and good stability.