Synthesis And Properties Of Diaryl Ketone Type Fluorescent Materials

Organic light-emitting diode（OLED）has attracted much attention due to its advantages of high efficiency,light weight and high color quality in display applications.However,most of the reported traditional fluorescent materials and thermally activated delayed fluorescence（TADF）emitters require complicated host-guest doping techniques in actual OLED application to avoid concentration quenching and exciton annihilation.At the same time,the doped OLEDs based on TADF emitters often show serious efficiency roll-offs at high current density,which is an important issue to be solved urgently.In order to simplify the preparation process and improve the efficiency stability of the device,it is of great significance to develop undoped OLEDs.The emergence of aggregation-induced emission（AIE）materials provides a solution to this issue,and their use can greatly alleviate efficiency roll-off caused by concentration quenching in OLED devices.However,till now emitters showing both AIE and TADF characters are rare,and the relevant mechanism is still unclear.In this thesis,AIE emitters with AIE-active tetrastyrene（TPE）groups and fluorophores with novel diaryl ketone（phenyl（2-phenylimidazo[1,2-a]pyridin-3-yl）methanone）acceptors have been reported.The structures of the molecules were determined by means of nuclear magnetic resonance and mass spectrometry.Their properties were fully characterized by ultraviolet-visible absorption,steady-state and transient photoluminescence,electrochemical study,thermal analysis and they were applied as emitter in OLEDs.In the first chapter,we introduced the development of OLEDs and the phenomenon of AIE,and summarized the mechanism,phenomenon and research progress of AIE and TADF materials.Materials with both AIE and TADF features are reviewed,and the research idea and molecular design strategy are proposed.Because TPE has many interesting chemical and physical properties,it can be not only used as an electron transfer catalyst,but also its rich electrochemical and excited state properties provide an excellent research model for energy transfer.On the other hand,the extendedπ-system of TPE is also an important candidate for various organic optoelectronic and optomechanical switches.Therefore,in the second chapter,we reported the design and synthesis of three AIE luminophores featuring D-π-A-π-D configuration based on carbazole-benzoyl substituted TPE derivatives TPE-BZ-Cz,TPE-2BZ-Cz,TPE-3BZ-Cz.At the same time,their photophysical properties and electroluminescence（EL）characteristics were studied.These luminophores exhibited good AIE performance and high solid-state fluorescence quantum yield.In addition,as the number of donor groups increases,the emission wavelengths of these three luminophores,whether in solution or in solid state,showed negligible changes.These three luminophores showed solvochromism and negative solvent kinetic effects in different solvents.More interestingly,as the number of carbazole-benzoyl groups increases,its thermal and morphological stability showed regular changes.Further EL study showed that the performance of TPE-3BZ-Cz based undoped OLED devices was superior to the other two emitters.In Chapter 3,we designed and synthesized three new aggregation-induced delayed fluorescence（AIDF）luminophores:pipd-BZ-PXZ,pipd-BZ-PTZ,and pipd-BZ-DMAC,bearing D-A asymmetric skeleton with novel（phenyl（2-phenylimidazo[1,2-a]pyridin-3-yl）methanone）diaryl ketone acceptors.Due to the strong intramolecular charge transfer（ICT）effect,pipd-BZ-PXZ and pipd-BZ-PTZ exhibit orange to red emission in solutions and neat films.In order to compare their EL performance,we fabricated two sets of devices with undoped and doped profiles.Undoped devices exhibited moderate performance.The current efficiency and external quantum efficiency（EQE）of non-doped devices based on pipd-BZ-PXZ are 19.86 cd·A^-1 and 7.04%,respectively.At 1000 cd·m^-2,the efficiency roll-off is only 2.3%,which is one of the smallest efficiency roll-off among the reported AIDF-OLEDs with emission wavelengths exceeding 570 nm.The doped devices showed good performance.The current efficiency and EQE of the doped devices based on pipd-BZ-PXZ are as high as55.41 cd·A^-1 and 15.77%,respectively.