Synthesis And Performance Of Imide-based Small Molecule Luminescent Materials

As a new generation of lighting display technology,organic light emitting diodes(OLED)have the advantages of rich colors,self-luminous,thinness,bendable,low energy consumption,and low cost,which have attracted widespread attention in the material industry.As the core material of the light-emitting layer of the OLED devices,small organic light-emitting molecules have attracted a lot of research interesting due to their advantages such as easy structure modification,easy purification,easy processing,and biocompatibility.However,most small light-emitting molecules show aggregation caused quenching(ACQ)in thin-film and solid state,which limits their application in OLEDs.On the contrary,the luminescence intensity of materials with aggregation-induced emission(AIE)performance increase at high concentration or aggregation state.The emergence of AIE provides a feasibility turning point for breaking through the shackles in the development of traditional light-emitting small molecules.Therefore,the new organic light-emitting materials with AIE properties were designed and synthesized that is very important to promote the development of OLED.In this thesis,1,8-naphthalimide(NI)were used as the basic group,and different groups were used to modify at different positions to improve the performance of luminescent materials and obtain small luminescent molecules with AIE performance.We designed a series of new luminescent materials with simple structure,low cost and high yield,and discussed the properties of the compounds.Then the performance parameters such as photoluminescence,electrochemical,thermal stability,fluorescence lifetime and quantum yield were compared and analyzed.The specific work content includes the following three parts:In the first system of the thesis,the compounds of SNI-Cz and SNI-DCz were designed and synthesized that 1,8-naphthalimide group as the molecular skeleton and N-phenylcarbazole group as the electron-donating unit.The two molecules have good thermal stability.The fluorescence emission peaks of SNI-Cz and SNI-DCz at 373 nm and 535 nm with near-ultraviolet and green light in solution were,respectively.The redox activity of SNI-Cz and SNI-DCz were investigated by using cyclic voltammetry(CV),the HOMO and LUMO levels of SNI-Cz were-5.80 and-2.45 e V,respectively,and those of SNI-DCz were-5.36 and-2.58 e V,respectively.The solid-state fluorescence quantum yields of SNI-Cz and SNI-DCz were 8.21%and 83.65%,respectively.The distribution of electron cloud of compounds was obtained by DFT.Both molecules have a distorted spatial structure.The carbazole group and the 1,8-naphthimide skeleton were in a nearly vertical conformation in space,which can effectively weaken the ACQ caused by the intermolecular accumulation in the solid state.By testing the fluorescence emission of SNI-Cz and SNI-DCz in the DMF/H₂O mixed system,two compounds have the AIE capability.In the second system of the thesis,based on the previous system,the compounds SNI-XDS and SNI-DXDS with good thermal stability were designed and synthesized,and the diethylaminocoumarin group was used as the chromophore to further improve the luminescence intensity and quantum yield.Their correct structure was tested by NMR and HRMS,and they showed green or orange fluorescence under ultraviolet light.The HOMO energy levels were-5.51 e V and-5.24 e V,while their LUMO energy levels were-2.92 e V and-2.75 e V.The electron cloud distributions of the two compounds were obtained by theoretical simulation using DFT.The solid-state fluorescence quantum yields of SNI-XDS and SNI-DXDS were 58.92%and39.50%,respectively.The SNI-DXDS showed relatively low solubility in common organic solvents which needed to be further optimization will be designed.In the third system of the thesis,based on the studies of the above two systems,the butterfly-shaped luminescent materials DNI-Cz and DNI-TPA were synthesized to solve the problems of weak luminescence or poor solubility.The two compounds used bibranched naphthalimide group the core unit,and N-phenylcarbazole or triphenylamine groups as the electron donor unit.The system aims to use the twisted structure of molecules to make compounds have certain AIE properties,limit molecular aggregation,improve the stacking morphology between molecules,and improve their solid-state luminescence performance.The structures were confirmed by NMR and MS.Both compounds showed good thermal stability.The fluorescence emission peaks of DNI-Cz and DNI-TPA in solution were at 538 nm and 600 nm,respectively,and showed yellow-green light and red light under ultraviolet light.Their HOMO and LUMO energy level were-5.33 e V/-5.36 e V and-2.59 e V/-2.99 e V respectively.The electron cloud distribution of the two compounds were calculated by DFT.The solid-state fluorescence quantum yields of DNI-Cz and DNI-TPA were 81.32%and79.09%,respectively.The fluorescence test was carried out in the DMF/H₂O mixed solution system,and the results showed that both compounds have the AIE capabilities.