Design And Synthesis Of Thermally Activated Delayed Fluorescence Materials Based On Carbazole-Benzene Cyanide

Solution-processed organic light-emitting diodes(Organic light-emitting dioes)have excellent performance,which can achieve large-scale,flexible,high-quality,self-luminous and other characteristics.It has great market potential in display panel and lighting field.Since OLEDs were first reported by Eastman Kodak in 1987,the improvement of OLEDs device performance has been an important research direction in academia.The choice of luminescent materials is the main factor affecting the performance of OLEDs.As the first generation of luminescent materials,traditional fluorescent emitters can only achieve 5%external quantum efficiency(EQE),which greatly limits the rapid development of fluorescent materials.The emergence of phosphorescent materials improves the emission efficiency of the device,but it has disadvantages such as high price,complex synthesis proces.Thermal activated delayed fluorescent materials as the third generation luminescent materials,the internal quantum efficiency(IQE)can reach 100%,which has become a hot topic in OLEDs field and has experienced rapid development.TADF materials break through the technical bottleneck of phosphorescent materials and become a low-cost and alternative material to expensive phosphorescent emitters.The development of organic light-emitting diodes in the field of display and lighting,luminous efficiency,stability and cost are factors that need to be considered in the preparation of high-efficiency OLEDs..The blue TADF material can effectively use singlet excitons and has the advantage of low cost.It is currently one of the best light-emitting materials in the preparation of OLEDs,but there are few blue TADF materials reported at present.Therefore,there is an urgent need to design low-cost,high-performance blue light emitting materials to achieve lighting under high-brightness work.The main content of this paper is to design and synthesize molecules with thermal activation delay properties,and test their photoelectric properties and thermal stability properties,then prepare OLEDs through a wet process to study the electrolu-inescence properties.The specific content is as follows:(1)Two molecules,4TCzBN-o-PhCz and 4TCzBN-o-MCP were synthesized by using pentafluorobenzyl cyanide as the receptor unit and tert-butyl carbazole as the donor unit,which using oxygen bridge to connect the fluorescent guest fragment and the host fragment.To explore the influence of different object groups connected by?key on device performance,photophysical,thermodynamic,morphological,electrochemical and device properties were characterized,.The results show that the introduction of oxygen bridges to connect the host and guest can avoid the phase separation in physical doping and improve the film-forming performance and stability of the material.The energy transfer between the host and guest will inhibit the concentration quenching process and improve the exciton utilization rate.The4TCzBN-o-MCP have excellent blue emission,AIE phenomenon and fluorescence quantum yield.The performance of the device OLEDs treated with non-doped solution based on 4TCzBN-o-MCP is obviously improved.The current efficiency(CE)is 24.9 cd A^-1,maximum external quantum efficiency(EQE)is 8.0%,power efficiency(PE)is 19.5 lm W^-1,these results demonstrate that connecting fluorescent host-guest segments through oxygen bridges may provide a new design concept for designing more efficient blue TADF emitters.(2)The 4BrCzBN,4BrCz-Cz were synthesized by using tetrafluorobenzyl cyanide as the receptor unit and carbazole as the donor unit,which encapsulation of luminescent nuclei through alkyl chains.And two new molecules were systematically tested by introducimng halogen atomic bromine.The results show that the changes of bromine atoms and peripheral branches will not affect the luminescence properties of the material.The introduction of the alkyl chain not only enhances the solubility of the molecules,the resistance to isopropanol corrosion and the film-forming properties of the molecules,but also gives the molecules a significant AIE phenomenon,which is more helpful for the wet process to prepare OLEDs.Compared with 4CzBN,the introduction of bromine atoms reduces?E_ST,and the energy levels of HOMO and LUMO are effectively separated.The OLEDs prepared with 4BrCzBN and 4BrCz-Cz as host materials and doped with 30%4Cz IPN,among which 4BrCzBN has the highest external quantum efficiency 4.2%,and the maximum brightness of 4BrCz-Cz is 10360 cd m^-2,which provides an idea for the design of wet process OLEDs through the concept of packaging.