| Organic electroluminescent devices(OLED)have received attention from since they came out.Organic electroluminescent material is one of the key factors affecting device performance.Currently,thermally activated delayed fluorescence(TADF)emitters have great potential,which are used to be next-generation luminescent materials.It captures triplet excitons through an effective up-conversion process,and theoretically achieves 100%exciton utilization efficiency.The small Singlet-Triplet Energy Gap(?EST)between the lowest singlet excited state(S1)and the lowest triplet excited state(Ti)is the key to molecular design,although the design of Donor-Acceptor(D-A)type molecules can get a smaller ?EST,however,to achieve a more stable and efficient TADF OLED,its molecular design and selection of structural unit remain to be discussed.In the field of high-cost blue light materials,the paper takes TADF emitters in the donor-bridge-acceptor configuration with naphthyl as the ? bridge as the research object and discusses the influence of the change in donor or acceptor on the properties of TADF materials,in order to expect stable and efficient TADF OLED.The paper is expected to provide more references for molecular design idea and the selection of each part of the group.The paper includes four chapters.The first chapter briefly introduces the development and research status of organic electroluminescent materials and thermally active delayed fluorescent materials,discusses the key factors and design strategies that need to be considered in the molecular design of TADF,and introduces the main content and innovations of the paper.The second and third chapters are the experimental parts.The donor unit,the acceptor unit,and the bridge unit are changed to discuss the influence of the change on the charge distribution and optical properties.The fourth chapter is a summary of the full text,and prospects for the future development of blue TADF OLED.The main research contents are as follows:(1)Use naphthalene as the ? bridge and 9-phenyl-9H-carbazole as the donor unit,introduce D/A units at the 1,8 positions of naphthalene and then design a series of TADF molecules with V-shaped D-?-A structure.The results show that the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)only have a slight overlap on the naphthalene ring of the bridging unit,and all three molecules have a small ?EST.With the volume of the introduced acceptor unit increasing,steric hindrance restricts the free rotation of the C-C bond to a certain extent,and slightly reduces the dihedral angle of the molecule.All three molecules have excellent thermal stability and electrochemical stability.With the enhancement of the D-A effect,the molecules has realized the regulation of the luminous color from dark blue to sky blue.The doped device prepared based on the target compound of 4-benzonitrile acceptor(CzPNPCN)has realized the ultra deep blue TADF OLED with CIEy?0.05.The work will provide more selectivity for the ultra deep blue TADF OLED luminescent material.(2)Use naphthalene as the ? bridge and 9,9',10,10'-tetraoxathien as the acceptor unit,introduce D/A units at the 1,8 positions of naphthalene and then design two TADF molecules with a V-shaped D-?-A structure with more distorted configuration.The results have shown that with the degree of conformational distortion of the introduced donor unit increasing,the degree of overlap of HOMO/LUMO energy levels greatly reduce,which make ?EST further decrease.The larger dihedral angle determines that the molecule has a highly distorted conformation,which can weaken the molecular interaction in the aggregate state.Both molecules have excellent thermal stability,morphological stability and electrochemical stability.Among them,the doped device prepared based on the target compound of 10-phenyl-10H-phenothiazine donor(PTZPN-TADATO)has realized deep blue light emission with CIEy?0.1,which will expand new types of deep blue TADF OLED materials. |
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