Construction Of Molecules And Study On Photoelectric Properties Of TADF Materials Based On Fluorinated Pyridine Derivatives Acceptor

In this paper,the research progress of thermally active delayed fluorescence（TADF）materials and their devices was reviewed.In view of the key scientific problems such as the lack of acceptor units for the construction of blue-light TADF materials,the lack of high-performance material systems,and the relatively low device efficiency,this paper carried out a research based on 5-（trifluoromethyl）pyridin-3-yl derivatives as acceptor units.Novel blue-light TADF materials were synthesized and their device properties were investigated.The following are the key research findings of this paper:5-（trifluoromethyl）pyridin-3-yl was used as the acceptor unit,then two different donor units of tert-butylcarbazole and acridine were introduced,and these donor and acceptor units were connected to the para or meta-positions of benzeneπbridge,respectively.Three D-π-A type molecules p-Cz Py CF₃-1,m-Ac Py CF₃-1 and p-Ac Py CF₃-1 were synthesized.The results reveal that the decomposition temperature of the three compounds exceeds 200℃when the thermal weight loss is 5%,showing that they have good thermal stability;The photoluminescence spectra in films and solvents of different polarities all show deep-blue to blue light emission;The compound m-Ac Py CF₃-1 exhibits the properties of TADF by the transient spectrum test;These three compounds were respectively used as guest materials of the light-emitting layer to fabricate vapor-deposited blue-light electroluminescent devices.Among them,p-Cz Py CF₃-1 has the highest device efficiency with a maximum external quantum efficiency(EQE_max)of 3.19%.4-（trifluoromethyl）pyridin-2-yl was used as the acceptor unit and the benzene ring was used as theπbridge,then the donor unit tert-butylcarbazole or acridine was introduced into the meta or para position to synthesize p-Cz Py CF₃-2,m-Ac Py CF₃-2 and p-Ac Py CF₃-2.The results show that these three compounds exhibit PL emission in the deep-blue to blue region in the film and solvents of different polarities,among which p-Cz Py CF₃-2 exhibits a high photoluminescence quantum yield（PLQY）of78.2%,and m-Ac Py CF₃-2 exhibits TADF characteristics;These three compounds were used as guest materials of the light-emitting layer to manufacture vacuum-evaporated blue-light electroluminescent devices,respectively.Among them,p-Ac Py CF₃-2 has the highest device efficiency with a maximum EQE_max of 4.46%.In order to increase the spatial block between the acceptor moiety and the benzeneπbridge,thereby reducing the intramolecular non-radiative transitions caused by the rotation of the single bond between the acceptor and the benzene ring,and regulating the charge transport ability between the donor and the acceptor to enhance device performance.3-（trifluoromethyl）pyridin-2-yl was used as the acceptor unit,then a class of D-π-A type molecules p-Cz Py CF₃-3,m-Ac Py CF₃-3 and p-Ac Py CF₃-3 were synthesized.The performance test results show that all three compounds exhibit deep-blue to blue light emission,and at the same time,m-Ac Py CF₃-3and p-Ac Py CF₃-3 have TADF properties;The organic light-emitting devices fabricated by vacuum evaporation method,among which p-Ac Py CF₃-3obtains the maximum external quantum efficiency of 6.57%.