Synthesis And Optoelectronic Properties Of Thermally Activated Delayed Fluorescent Materials Based On Purine Or Difluoroboron β-Diketone Acceptors

In recent decade,organic light-emitting diodes（OLEDs）have been commercialized in flat panel displays and solid-state lightling applications because of their advantages of low power consumption,wide visual angle,fast response rate,etc.The performace of OLEDs is fundamentally dependent on the electroluminescent materials.Thermally activated delayed fluorescent（TADF）materials have been regarded as one of the most promising third-generation organic electroluminescent materials,mainly due to their 100%internal quantum efficiencies（IQEs）and metal-free molecular structures.To realize 100%IQEs,TADF emitters need to have small singlet-triplet splitting energies(ΔE_STs)to enable efficient reverse intersystem crossing（RISC）process from triplet to singlet states.To achieve smallΔE_STs,well separated frontier molecular orbitals（FMOs）are highly required.In this sense,appropriate electron donors（D）,acceptors（A）and bridging moieties are generally adopted in the typical D-A structures to construct TADF emitters.This design strategy can ensure a good separation between the highest occupied molecular orbital（HOMO）and the lowest unoccupied molecular orbital（LUMO）and thus result in smallΔE_STs.Therefore,new efficient TADF materials can be constructed by selecting electron acceptor units.In chapter 1,we firstly gave a brief introduction of the background,basic principle,device structure and processing method of OLEDs,and then the luminescent mechanism,developing progresses,current situation and design strategy of organic electroluminescent materials were introduced.Finally,we proposed our design tactics for the new TADF emitters in this thesis.In chapter 2,a purine moiety was firstly introduced as an electron acceptor unit for TADF emitters.Two TADF emitters（1PXZP and 2PXZP）were successfully synthesized and characterized.2PXZP with an additional donor exhibited better thermal stability,tunable photophysical and optoelectrical properties without changing the electrochemical properties.In comparison with 1PXZP,2PXZP had the smaller?E_STand higher photoluminescent quantum yield.Finally,the 2PXZP-based device achieved a better device performance with a maximum external quantum efficiency(η_ext)of13.8%.In chapter 3,difluoroboronβ-diketone and dimethyl acridine were uased as the electron acceptor and donor,respectively.Two red TADF emitters（1DMACPDOBF₂and 2DMACPDOBF₂）were successfully synthesized and characterized.In comparison with 1DMACPDOBF₂,2DMACPDOBF₂ with one more donor displayed the smaller?E_ST.The solution-processed OLED device based on 1DMACPDOBF₂ displayed a better device performance with a maximumη_ext of 5.64%.Moreover,the non-doped OLEDs based on these emitters exhibited near-infrared emissions with the main electroluminescent peaks in the range of 726-728 nm.