Synthesis And Properties Of Thermally Activated Delayed Fluorescence Polysiloxane Materials

Organic light-emitting diode(OLED)has been invented for more than 30 years.OLED has gradually become the mainstream material of upscale display and lighting because of its unique advantages.But it still faces the problems such as high cost,low efficiency and poor stability.As the representative of the third generation OLED materials,thermally activated delayed fluorescence(TADF)materials achieved 100%of internal quantum efficiency through the characteristic of reverse intersystem crossing(RISC).At the same time,they can also be prepared with pure organic materials,which have the potential of low cost and large area production.Polysiloxane is suitable for solution processing,and has the advantages of thermal stability,adjustable energy level,low dielectric constant and main chain conductivity.It is widely used in OLED as the host,excitons transport and excitons barrier materials,but is rarely used in the luminescent layer.In Chapter 2,a series of TADF polysiloxanes with different donor/acceptor ratios were synthesized by using dimethylaacridine/cyclohexyltriazine as donor/acceptor and mercaptopropylsilane as main chain,which have good film-forming property,low energy level,first singlet-triplet energy level gap(ΔEST)which less than 0.0168 eV and sky-blue emission.The sulfur,oxygen and other heteroatoms and heavy atoms in the main chain of polysiloxane can greatly enhance the spin-coupling of the excited state of the emitting unit,making the polymer have a RISC rate constant(kRISC)of the order of 107.Finally,this series of polysiloxanes obtained the highest photoluminescence quantum yield(PLQY)of 10.33%.In Chapter 3,two alternating polymerized TADF polysiloxanes with different ratios of donor/acceptor were obtained by adjusting the end groups of siloxane and changing the polymerization method.The composition of the polymers is more uniform by dispersing the emitting units,which reduces defects such as exciton quenching caused by aggregation.Alternating copolymers have narrower fluorescence emission peaks and higher kRISC than random copolymer materials with the same donor/acceptor ratio.Finally,the PLQY of these two polymers was significantly improved,reaching 29.88%and 17.73%,respectively.