Design,Synthesis And Performance Research Of Pure Thermally Activated Delayed Fluorescence(TADF) Materials

In rencent years,organic light-emitting diode(OLEDs)has received extensive attention by scientists due to its superior advantages compared to the traditional flat panel display and lighting.In preparing and optimizing OLEDs,the choice of luminescent materials plays an important role.Pure organic emissive materials with thermally activated delayed fluorescence(TADF)properties have been studied extensively as the emitters or emitting dopants in OLEDs,because of their diverse structure designs,adjustable colours,low costs,simple synthetic methods and so on.Because carbazole moiety has relatively rigid structure,high thermal stability,high triplet energy level and excellent hole-transporting abilities,it has been used in the designing of many optoelectronic materials.In this work,a series of new type of thermally activated delayed fluorescence(TADF)compounds containing carbazole moieties have been designed,and the principal results are summarized as follows.1.Two compounds with benzonitrile groups as eletron acceptor and 3,6-di-tert-butyl-carbazoleas electron donor,2,6-(3,6-di-tert-butyl)carbazole benzyl cyanide(2tBuCzBN)and 2,3,5,6-tetrakis(3,6-di-tert-butyl)carbazole-4-fluorobenzonitrile(4tBuCzFBN),were prepared.These two compounds show typical TADF with blue emissions(λPL=432 or 474nm),and good thermal stability,solubility and film-forming.The compound 2tBuCzBN was used as emitter dopant into the host material of mCP in an OLED device and the maximum external efficiency is 3.9%.2.Two novel thermally activated delayed fluorescent materials(MePhS)2tBuCz and MePhSO2Cz were synthesized.In these compounds,aromatic sulfide group and acromatic sulfone group were designed as the electron acceptor units,and carbazole and tert-butyl carbazole were used as the electron donor units.Both compounds have very high decomposition temperatures and good solubility in common solvents.The photoluminescence quantum efficiencies of the compounds doped in PMMA are 10.8%and 40%and the maximum emission peak are at 446nm and 470nm for(MePhS)2tBuCz and MePhSO2Cz,respectively.3.Two compouds CzBN(4-S-Br)and CzBN(4-S-Py)in which 4-sulfide-substituted benzonitril units are designed as electron acceptor and the carbazole units as electron donors were synthesized.On one hand the introduction of bromine atoms in the acceptor to increase the coupling of the molecules in the track,on the other hand,the N atom was introduced into the benzene ring to increase the rigidity of the molecules.The photoluminescence quantum efficiencies in toluene are about 85%,and the lifetimes are about 5μs.The two compounds were doped with 10 wt%in the host material mCP,spin-coated to form a luminescent layer,and were fabricated into OLED devices.We obtained the blue device B and the cyan-green device C,respectively.Both devices have a brightness of about 3200 cd/m2,and the external quantum efficiencies of the devices are 12%and 6.5%for B and C,repsectively.