Design,Synthesis And Properties Of Boron-Containing Thermally Activated Delayed Fluorescence Materials For Organic Optoelectronic Applications

Thermally activated delayed fluorescence（TADF）materials have received extensive attention and research in the fields of organic light-emitting diodes（OLEDs）,bioimaging,etc.due to their absence of expensive metals,efficient exciton utilization,and diverse molecular structure design approaches.However,TADF materials based on the principle of donor-acceptor（D-A）structure design have defects such as aggregation quenching and low color purity,which limit the further development and application of TADF materials.In this thesis,boron-containing organic functional materials with special optoelectronic properties are designed and constructed by utilizing the electron-deficient and Lewis acid properties of boron atoms.The luminescence color of TADF materials was effectively regulated,TADF molecules with excellent purity and high purity were designed,and the host-guest two-component organic long afterglow was designed.The research contents are as follows:（1）The deep red TADF molecules were obtained by increasing the degree of molecular conjugation,which would lead to poor solubility of the material,making it difficult to achieve efficient solution-processed device.In this chapter,two kinds of deep red light-emitting TADF molecules were successfully prepared by cyano functionalization strategy to control the electron-withdrawing ability of boron-containing acceptor units.In the thin film,its emission peaks are at 680 and 718 nm,respectively,and it exhibits good solubility in common organic solvents.Applying it to a solution-processed OLED device,a highly efficient red light TADF-OLED was successfully obtained,with a turn-on voltage of 4.2 V,a maximum external quantum efficiency of7.4%,and an electroluminescence peak at 660 nm,which is one of the best device performance in the current deep red TADF-OLED.This study provides an efficient material design strategy for the design of efficient solution-processable organic optoelectronic materials,especially in the design of deep red TADF molecules.（2）For the TADF materials based on the D-A structure,the molecular structure relaxation is obvious,the emission peak spectral bandwidth is wide,and the color purity is low.In this chapter,a novel green narrow-band TADF molecule was designed and synthesized by introducing sulfur atoms into the boron-nitrogen multiple resonance system and increasing the degree of conjugation of the molecule.The study found that the multi-resonance effect（MR）effect extended to the CT delocalized area,and successfully achieved a smallerΔE_ST and higher luminous efficiency.And it is found that the amount of charge transfer and structural conjugation increased can realize the effective regulation of the luminescent color of the material.The vacuum-evaporated OLEDs based on MR-TADF molecules obtained green emission with a maximum external efficiency of 8.4%.This method of introducing sulfur atoms into the BN resonance system is effective in designing MR-TADF molecules with different color gamuts.（3）There are strong intramolecular/intermolecular interactions in organic single-component afterglow materials,resulting in a large full width at half maximum（FHWM>100 nm）and low color purity of most afterglow materials.In this chapter,MR-TADF with high luminous efficiency,narrow emission band,and high color purity was used as the guest molecule,and polycarboxyl and methyl cholic acid was used as the host molecule.Through simple melt-mixing for host-guest doping,narrow-band two-component organic afterglow materials were successfully obtained.The low-concentration doped films can effectively suppress molecular vibrations,reduce nonradiative transitions,and isolate water and oxygen to prevent triplet excitons from being quenched.The afterglow peak of organic afterglow material is 498 nm,its full width at half maximum is only 32nm,the afterglow lifetime reaches 1850 ms and the quantum yield is as high as 89.3%.For the first time,a high-efficiency and long-life organic narrow-band afterglow material has been obtained.This work provides a feasible way for the regulation of the spectral band width of organic afterglow materials.