Design,Synthesis And Studies Of Thermally Activated Delayed Fluorescent Material And Solution Processed Devices Based On Benzonitrile Carbazole

Organic light-emitting diodes（OLEDs）have attracted more attention due to self-luminescence,short response time,wide viewing angle,low cost,energy consumption and flexible production.At present,OLEDs has achieved great development and has been widely used in full-color,large-area flat-panel displays.In generally,OLEDs materials include traditional fluorescent materials,phosphorescent materials and thermally activated delayed fluorescent materials（TADF）.Due to the spin inhibition of the triplet excitons of traditional fluorescent materials,thetheoretical internal quantum efficiency is only 25%,which hinders the device performance of traditional fluorescent materials.By introducing heavy metals,phosphorescent materials use the heavy atom effect to improve the molecular spin-orbit coupling,which can use triplet excitons that were initially forbidden,breaking the limitation of quantum efficiency below25%in traditional fluorescent materials.Its maximum internal quantum efficiency has reached 100%,so the performance of phosphorescent light-emitting devices is better than traditional fluorescent materials generally.However,phosphorescent materials usually use precious metals,their high cost limits the development and application of phosphorescent materials.TADF materials triplet excitons can transformed into singlet state by radiative transitions,thereby enabling triplet excitons can be used.TADF materials can achieve 100%internal quantum efficiency without doping precious metals.Compared with traditional fluorescent materials and phosphorescent materials,TADF materials have low cost and high efficiency,and has achieved good development in recent years.Therefore,based on previous studies,several TADF materials have been designed and synthesized,and a series of studies have been carried out to obtain highly efficient TADF materials.（1）Ensure that the luminous nucleus remains unchanged,5CzCN-SSP and 5CzCN-DSP were synthesized by changing the number of peripheral branches,the peroperties including thermodynamics,optics,morphology,and electricity chemical and device performance of previously synthesized molecules 5CzCN-QSP was also investigated.The results show that the addition of peripheral branches through the non-conjugated alkyl chain will not change the luminescent properties of the luminescent core,but it increase the solubility of the molecule,resistance to corrosion by isopropanol and film-forming properties.The device results show that the fully solution self-hosted OLED prepared with 5CzCN-QSP as the light-emitting materials has better luminous performance,and the power efficiency and external quantum efficiency has reached to 46.2 lm W^-1 and 20.1%respectively.Both are located in the excellent performance category of all-solution OLEDs,indicating that the addition of non-conjugated alkyl chains on the periphery of the light-emitting material can encapsulate the light-emitting nucleus,reduce the concentration quenching effect of the self-host light-emitting material,and has better resistance to solvent erosion.Dendrimer TADF materials are more conducive to the preparation of all-solution method devices,and provides a new design concept for the design of all-solution method self-host luminescent materials.（2）Based on the research in the previous section,blue light-emitting material 4CzCN-SP was synthesized by changing the design of the internal light-emitting nucleus,and the morphological stability,thermal stability,and resistance to isopropanol of the blue light molecule was studied.The 4CzCN-SP also has good resistance to solvent attack,indicating that encapsulation of the light-emitting nucleus through non-conjugated alkyl chains connected to the dendrite group can effectively increase the solubility of the molecule and solvent resistance.（2）Using 4CzCN-SP as emitter to prepare a full-solution OLED device,its power efficiency and external quantum efficiency are 21.0 lm W^-1and 14.1%,respectively,which provided a new method for achieving high-efficiency light-emitting full-solution blue OLED.（3）Thermal cross-linked luminescent materials 3CzCN-DV and 3CzCN-O-DV containing styrene units and benzene cyanide units were designed and synthesized.The structures of two molecules were characterized by ¹H NMR,¹³C NMR,Elemental analysis and Mass spectrometry,and their electrochemical properties,thermodynamic properties,photophysical properties and morphological stability were measured.The results showed that compared with 3CzCN-DV,the roughness of 3CzCN-O-DV was decreased from 0.74 nm to 0.48 nm,and the curing temperature of 3CzCN-O-DV was decreased from 228 ^oC to 188 ^oC.Therefore,the introduction of flexible alkyl chains into thermally cross-linked molecules leads to the change of molecular configuration,which does not change the photophysical properties and thermally activated delayed fluorescence characteristics of molecules,and can effectively reduce the curing temperature of thermally cross-linked molecules,providing new ideas for the development of new thermally cross-linked luminescent materials.It is expected that thermally cross-linked luminescent materials will be used as luminescent layer materials in solution electroluminescent devices.